Daria Kasatkina claimed the fourth title of her career after Margarita Gasparyan retired in the second set of the St Petersburg Ladies Trophy final with a back injury.

Kasatkina, who becomes the first player to win two WTA tournaments in 2021 having claimed the Phillip Island Trophy last month, was leading 6-3 2-1 when Gasparyan pulled out.

Gasparyan initially took a medical timeout after losing her first two service games of the match to trail 4-1 before eventually retiring after dropping her serve early in the second set.

Kasatkina's triumph meant she became the first player to win both WTA 500 events on Russian soil, previously claiming the 2018 Moscow title at this level.

The former top-10 player has endured a dip in recent seasons but will be back in the top 50 on Monday, while wildcard Gasparyan's maiden WTA 500 final means she returns to the top 100.

Kasatkina dropped the opening set in her quarter-final and semi-final matches but then swept through the next two sets emphatically on each occasion.

"I'm proud of how I was able to manage the pressure," Kasatkina said, quoted on the WTA website. "I felt differently during this tournament and I'm really proud of that."

Leylah Fernandez and Viktorija Golubic will go head-to-head in the Monterrey Open after progressing on Saturday.

Canadian teenager Fernandez reached her second career WTA Tour singles final thanks to a 7-5 7-5 win over seventh seed Sara Sorribes Tormo.

The 18-year-old Fernandez – whose first final came via last year's Mexican Open in Acapulco, where she lost – converted six of nine break points and hit 35 winners.

Standing in Fernandez's way is Switzerland player Golubic.

Golubic upstaged eighth seed Ann Li 6-2 6-4 to become the first qualifier to advance to the Monterrey Open final in the tournament's history.

The 28-year-old Golubic also reached the Lyon Open final two weeks ago – beaten by Clara Tauson.

Daria Kasatkina and Margarita Gasparyan fended off two of the great stalwarts of Russian tennis to set up a final showdown at the St Petersburg Ladies Trophy.

Kasatkina recovered from a slow start to overcome fourth seed and two-time grand slam winner Svetlana Kuznetsova, after Gasparyan saw off former Wimbledon and US Open runner-up Vera Zvonareva.

Zvonareva, 36, and Gasparyan, whose promising career has been disrupted by injury, were both allocated wildcard entries to the tournament and seized advantage to reach the last four.

Gasparyan, a 26-year-old whose single-handed backhand is an unusual sight in modern tennis, came through the clash with Zvonareva a 6-3 7-6 (11-9) winner to reach her first final at WTA 500 level.

The world number 126 will tackle former top-10 star Kasatkina for the title, after the 23-year-old Barcelona resident scored a remarkable 1-6 6-0 6-2 win over Kuznetsova in the second semi-final.

It was a flat Kasatkina who surrendered the opening set, but she then dashed off eight games in a row, levelling the match and surging to a 2-0 lead in the decider, knocking the stuffing out of 35-year-old Kuznetsova's challenge.

Kasatkina, a 23-year-old with more variety than most, had also dropped the first set 6-1 in her quarter-final win over second seed Veronika Kudermetova on Friday before finding her best game.

She said on Amazon Prime: "Well, why not, if losing the first set will guarantee me victory, why not?"

Kasatkina, the eighth seed this week, won the Phillip Island Trophy in Melbourne last month so is chasing a second WTA title of the year.

She is relishing the clash with Gasparyan, saying: "It's cool to have players of different styles. Tomorrow's a final so you've just got to go out there and try to show your best tennis."

An all-Russian final was already guaranteed, given the host country locked down all four semi-final places, and it will be the 30th such WTA title match.

Eighth seed Ann Li toppled the top remaining seed Zheng Saisai in the quarter-finals of the Monterrey Open on Friday, throwing the field wide open.

Li triumphed 7-5 6-1 over third seed Zheng, who held the highest rank of all remaining players after Sloane Stephens and Nadia Podoroska's first-round exits.

World number 52 Zheng struggled to win on her first serve, with Li converted five of seven break points.

American Li, who is ranked 72nd in the world, will next face Swiss qualifier Viktorija Golubic, who beat Russia's Anna Kalinskaya 6-2 6-4.

On the other side of the draw, Canadian Leylah Fernandez defeated Slovakia's Viktoria Kuzmova 7-5 6-3 and will face seventh seed Sara Sorribes Tormo in the other semi-final.

Sorribes Tormo, who is now the highest ranked remaining player, defeated Anna Karolina Schmiedlova 6-3 7-5.

Daria Kasatkina and wildcard Margarita Gasparyan sank the top two seeds at the St Petersburg Ladies Trophy, where the semi-finals will be all-Russian showdowns.

Ekaterina Alexandrova, the number one seed, fell 6-2 7-5 to Gasparyan, before former top-10 star Kasatkina continued her recent revival by landing a 1-6 6-1 6-2 victory against Veronika Kudermetova.

Friday marked the first time at a WTA tournament that as many as seven of the final eight players have been Russian, and the day's opening clash produced a significant upset.

It was a valid reminder of what might have been for world number 126 Gasparyan, who like Alexandrova is 26 years old but has struggled massively with injuries over the years.

Gasparyan was particularly helped by her superior form on first serve in the opening set, putting 72.7 per cent in court to 44 per cent by her opponent and winning 75 per cent of points when landing that delivery.

A topsy-turvy second set saw a total of seven breaks between the two players, but Gasparyan's 4-3 advantage in that respect helped her clinch a first WTA 500 semi-final appearance.

Up next for her is 36-year-old Vera Zvonareva, the former world number two who beat Anastasia Gasanova 6-3 6-1, saving six of seven break points en route to victory.

Romania's Jaqueline Cristian was the final non-Russian player left in the draw and she certainly tested Svetlana Kuznetsova, but ultimately the 35-year-old fourth seed prevailed 6-7 (5-7) 6-3 6-3.

Next for former US Open and French Open winner Kuznetsova will be Kasatkina, who rounded off the day by shaking off a slow start to look highly impressive against second seed Kudermetova.

The 23-year-old Kasatkina has endured a couple of lean years since entering the top 10 in October 2018 but landed a title last month at the Phillip Island Trophy.

Asked about how she came back from being trounced in the opening set by Kudermetova, Kasatkina said on Amazon Prime: "I think it's just women's tennis and this is what tennis is all about.

"It took me some time to get into this match but at the end I won it."

As for how Saturday's clash with Kuznetsova might play out, Kasatkina said: "We trained many times together but never played in an official match so it's hard to say."

Third seed Zheng Saisai comfortably accounted for countrywoman Zhu Lin to reach the quarter-finals of the Monterrey Open on Thursday.

Zheng, who is ranked 27th in the world, triumphed 6-1 6-2 in a dominant display where she was seldom challenged.

In the last eight, Zheng will face eighth seed Ann Li, who overcame Slovenian Tamara Zidansek 6-4 6-3 at the WTA International tournament.

Zheng is the highest remaining seed left standing in the draw after the first-round exits of top seed Sloane Stephens and Nadia Podoroska.

Russian qualifier Anna Kalinskaya continued her good run with a 6-4 6-3 victory over Nina Stojanovic and she will next face Viktorija Golubic in the quarters – the latter topped Lauren Davis 6-3 6-1.

A record seven Russians will contest the quarter-finals of the St Petersburg Ladies Trophy after victories for seeds Veronika Kudermetova and Daria Kasatkina on Thursday.

Number two seed Kudermetova edged past Kamilla Rakhimova 7-5 3-6 7-6 (7-5), while eighth seed Kasatkina also needed three sets to see off Aliaksandra Sasnovich 5-7 6-3 7-6 (7-2). 

Wildcard Margarita Gasparyan held off Katerina Siniakova 6-4 6-4 and qualifier Anastasia Gasanova shocked fifth seed Anastasia Pavlyuchenkova 1-6 7-6 (10-8) 7-6 (7-4). 

They joined fellow Russians Vera Zvonareva, Ekaterina Alexandrova and Svetlana Kuznetsova in the last eight, with Romanian qualifier Jaqueline Cristian also in the line-up.

The previous highest number of Russians in a WTA quarter-final line-up was six, set at Moscow 2005 when Kuznetsova was joined by Dinara Safina, Elena Dementieva, Maria Sharapova, Anastasia Myskina and Elena Likhovtseva.

The last time a single nation had as many players at this stage of a WTA event was in Oakland in 1993 when the United States produced seven of the eight quarter-finalists.

Canadian teenager Leylah Fernandez booked her spot in the Monterrey Open quarter-finals after easing past Kristina Kucova.

Fernandez cruised into the last eight of the WTA International tournament on Wednesday by defeating Slovakia's Kucova 6-1 6-4 in Mexico.

Kucova had eliminated top seed and 2017 US Open champion Sloane Stephens on Tuesday, but she was no match for the 18-year-old Fernandez midweek.

Next up for Fernandez is Viktoria Kuzmova, who beat lucky loser Harriet Dart 6-4 6-3.

Spanish seventh seed Sara Sorribes Tormo did not have to take to the court, benefiting from a walkover after Kaja Juvan withdrew.

Sorribes Tormo will face Anna Karolina Schmiedlova, who outlasted Jasmine Paolini 2-6 6-2 6-2.

Russian duo Svetlana Kuznetsova and Vera Zvonareva recorded contrasting victories on home soil to reach the last eight of the St. Petersburg Ladies Trophy.  

Kuznetsova - who has won both the French and US Open during her distinguished career - needed just over an hour to get past teenage qualifier Wang Xinyu by a 6-1 7-5 scoreline.  

The 35-year-old converted six of the nine break-point opportunities she created, though was made to work for her win in the second set having previously taken nine of the opening 10 games.  

After failing to serve out for the match when 5-3 ahead, the fourth seed eventually prevailed when recording a break of her own with the score at 6-5.  

Zvonareva, meanwhile, was on court for three hours and 10 minutes as she produced an impressive upset, knocking out third seed Fiona Ferro 6-7 (8-6) 7-5 7-6 (7-2).  

"We both were fighting for every point, trying to hang in there. I think I was able to play some good tennis when it mattered, and I'm happy with the win of course,” Zvonareva said after being involved in the longest match in the history of the tournament, per the WTA's website.  

The 36-year-old came out on top in a deciding tie-break having been unable to hold on to an early 2-0 lead in the set.  

Anastasia Gasanova and Katarina Zavatska had set a new record for the longest contest earlier on Wednesday, the former eventually prevailing 6-2 6-7 (8-6), 7-5 after three hours and four minutes in an eventful first-round tie.

Ekaterina Alexandrova is another Russian player to progress to the last eight, seeing off Tereza Martincova in straight sets.

In the final match, Romanian qualifier Jaqueline Cristian surprised Jelena Ostapenko 6-3 7-6 (11-9) to reach her first ever WTA 500 quarter-final, where her opponent will be Kuznetsova.

Former US Open champion Sloane Stephens has continued her torrid start to 2021 after crashing out in the first round of the Monterrey Open on Tuesday.

Stephens went into the Mexico event as top seed but lost to Slovakian world number 151 Kristina Kucova 6-2 6-2.

The 27-year-old American is now 0-4 to start the 2021 WTA Tour season and has won only one set all season.

Stephens, now ranked 48th in the world, only managed to win 32.4 per cent of points on her first serve, with Kucova converting seven of 14 break points in the match.

Second seed Nadia Podoroska was also a first-round casualty on Tuesday, going down 6-4 6-4 to Russian qualifier Anna Kalinskaya.

In the late match, Eugenie Bouchard went down to China's Lin Zhu 7-5 7-6 (6-3).

Daria Kasatkina fended off fast-rising star Clara Tauson at the St Petersburg Ladies Trophy as the Russian home favourite edged a clash of recent tournament winners.

Former world number 10 Kasatkina, who landed the Phillip Island Trophy title in Melbourne last month, came through a roller coaster second set against the qualifier to tie up a 6-4 7-6 (7-0) first-round victory.

Former junior world number one Tauson won the Lyon Open at the start of March, and the 18-year-old Danish player twice broke when Kasatkina was serving for the match to take their tussle to a tie-break that was then unexpectedly one-sided.

Having been jittery when serving at 5-4 and 6-5, Kasatkina found composure when it mattered to see out the match.

Tauson had won 13 consecutive matches, including qualifiers, and had reeled off 20 successive sets during that run, but Kasatkina interrupted the hot streak.

Three-time WTA tournament winner Kasatkina, seeded eighth this week, said on Amazon Prime: "You're right, I was nervous serving for the match, but I'm glad I could close out the match playing the tie-breaker.

"Sure, there is something to improve, but I don't want to talk about it right now. I'm going to talk to my coach about what I need to improve. She wasn't an easy opponent. She just won a tournament and I knew it was going to be a tough match, and a tough match it was."

Two 19-year-old qualifiers were also among Tuesday's winners, as Chinese player Wang Xinyu and Russian Kamilla Rakhimova safely went through to the last-16 stage.

Nao Hibino was a shock first-round casualty at the Monterrey Open, while fellow seed Ann Li advanced.

Seeded ninth for the WTA International tournament, Japan's Hibino was upstaged 3-6 6-2 6-3 by Jasmine Paolini on Monday.

American eighth seed Li, however, had no such trouble in her 6-3 7-5 victory over Arantxa Rus on the outdoor hard courts.

Coco Vandeweghe – the 2017 Australian Open semi-finalist – suffered another early exit in Mexico.

After being ousted by Mihaela Buzarnescu in the opening round in Guadalajara last week, former world number nine Vandeweghe was eliminated 6-3 6-2 by Canadian teenager Leylah Fernandez.

Fernandez will face either top seed Sloane Stephens or lucky loser Kristina Kucova in the second round.

Anna Karolina Schmiedlova, Nina Stojanovic, Viktoria Kuzmova, Lauren Davis and Tamara Zidansek also progressed from the opening round.

Jelena Ostapenko wasted little time in her opening match at the St Petersburg Ladies Trophy, while there were also wins for Aliaksandra Sasnovich and Vera Zvonareva in Monday's action. 

Ostapenko needed less than an hour to get past Paula Badosa, who caused an upset when the pair met at last year's delayed French Open. 

There was to be no Roland Garros repeat for Badosa, though, as she was swept aside 6-2 6-2.  

The sixth-seeded Ostapenko started her campaign impressively in Russia, producing 26 winners and just eight unforced errors. Her serve was also in good order, never giving her opponent a chance of a break. 

Sasnovich had to work a little harder, rallying from a set down to see off Ana Bogdan 2-6 6-2 6-1. Her reward is a clash with third seed Fiona Ferro, who received a bye through to the second round.

Zvonareva, meanwhile, progressed in straight sets against Arina Rodionova, the Russian dropping just four games during a contest that lasted one hour and 22 minutes.  

Victory was sealed at the second opportunity, a sliced backhand into the net by her opponent sending Zvonareva through to the last 32. 

Garbine Muguruza reached the final of the Dubai Tennis Championships after a gruelling victory over Elise Mertens on Friday.

The Spaniard saw six match points come and go in a battle lasting two hours and seven minutes before eventually closing out a 6-4 7-6 (7-5) win.

Having reached the final in Doha last week, where she lost to Petra Kvitova, Muguruza is the fifth player this century to reach back-to-back finals in the Middle East double, after Martina Hingis, Justine Henin, Caroline Wozniacki and Svetlana Kuznetsova.

The two-time major winner has now reached three finals in her past four tournaments and has won 17 matches in 2021.

Despite being ahead for much of the match, Muguruza was nonetheless pushed hard by Mertens, who fought back to beat Jessica Pegula in the quarter-finals after facing three match points.

She led by a set and 5-3 but Mertens continued to come up clutch at key points until Muguruza at last completed the job with a smash in the tie-break.

"You have to be all the time concentrated, otherwise she will come back," she said. "I didn't lose the focus even though I couldn't close it [at first] – I was just looking forward to the next opportunity.

"I didn't think I played bad on the match points. They were just tough points that didn't come to my side. She was very good in defence and on those points, I felt she brought her magic. But I was like, 'Okay, I'm playing well, sooner or later I will convert the match point'. I didn't lose the concentration or get too irritated."

Muguruza will face Barbora Krejcikova in the final, the Czech defeating Jil Teichmann 7-5 6-2.

Krejcikova saved 10 of 11 break points as she reached just the second Tour final of her singles career and has yet to drop a set at this tournament.

The world number 63 is the lowest-ranked singles finalist in history in Dubai, with that previous record held by Virginie Razzano, who was ranked 58 in the world when she lost to Venus Williams in 2009.

Elise Mertens came from behind to clinch a semi-final spot at the Dubai Tennis Championships but Coco Gauff bowed out on Thursday.

Mertens said she "just didn't want to let go" after coming back from the brink to end Jessica Pegula's fine run with a 5-7 7-5 6-0 victory.

The Belgian looked to be heading out when she faced a 5-2 deficit in the second set, yet saved three match points to force a decider.

"I kept on fighting and that was the spirit today," said world number 18 Mertens.

Former world number one Muguruza is Mertens' semi-final opponent, the Spaniard having come from a set down to beat third seed Aryna Sabalenka 3-6 6-3 6-2.

Muguruza lost out to Petra Kvitova in the final of the Qatar Open last week, but looks on top form as she closes in on another championship match.

Sabalenka fell foul of Muguruza in Doha, and the Belarusian was unable to gain revenge as the ninth seed earned a 16th win of the season.

There was to be no place in the last four for 16-year-old Gauff, who came up short against world number 54 Jil Teichmann.

Gauff, who defeated Teichmann twice in Australia in February, was broken to go 5-3 down in the first set and could not respond.

A second break in Teichmann's favour put Gauff on the back foot in the second, and the Swiss then saved three break points to nose into a 3-1 lead.

The contest was settled on Gauff's serve – Teichmann taking the match at the second time of asking to tee up a last-four clash with Barbora Krejcikova, who beat Anastasia Potapova 6-0 6-2 in a little over an hour.

Krejcikova was beaten in the doubles final last year, and has claimed her place in the singles semi-finals of a WTA 1000 event for the first time.