Serena Williams and Simona Halep started the season with straight-sets victories in Melbourne a week before the Australian Open gets under way.

Williams and Halep played in an exhibition event with a crowd of 4,000 watching on in Adelaide last Friday and they were back in competitive action three days later.

Legendary American Williams beat Daria Gavrilova 6-1 6-4 to move into the third round of the Yarra Valley Classic.

The fifth seed struck 27 winners to 15 unforced errors on Margaret Court Arena as she set up a meeting with Tsvetana Pironkova, who ousted Donna Vekic 1-6 6-4 6-2.

Williams said: "It was a good match for me. It wasn't easy at all. It was lots of rallies and lots of movement, and she's from here, so she obviously always plays hard. So it was really good and it felt good to clinch that in the end."

Third seed Karolina Pliskova, Petra Martic, Danielle Collins and Marketa Vondrousova also advanced to the last 16 on Monday.

Elsewhere, top seed Halep is through to the third round of the Gippsland Trophy following a 6-4 6-4 win over Anastasia Potapova.

Halep hit 23 winners and broke twice in each set in what was her first official match since October.

Elina Svitolina, the third seed, beat Andrea Petkovic 6-1 6-4, while Coco Gauff, Ekaterina Alexandrova and Jelena Ostapenko were among the other winners seven days prior to the start of the first grand slam of 2021.

Karolina Pliskova has crashed out of the Abu Dhabi Women's Tennis Open in the second round, while Coco Gauff was also eliminated.

Third seed Pliskova suffered a stunning 6-2 6-4 defeat to Anastasia Gasanova, a qualifier ranked at 292 in the world.

Pliskova fell to defeat in only 75 minutes on Saturday, the first time she had lost to an opponent outside of the top 50 in over a year.

Gasanova, 21, beat Mona Barthel in her WTA main draw debut this week and went on to save five of the six break points she faced to record an even bigger upset against Pliskova.

"It was not me on the court," a stunned Gasanova said after winning in her first match against a top-100 player, booking a last-16 clash against Sara Sorribes Tormo.

"I was so sure of myself. I'm really happy right now.

"I'm really surprised, but when I woke up today, I thought, 'Why not? Why can't I win this match?'

"Actually, I thought I would lose in qualies or something like that, but I just kept pushing myself, like, I need to win and I want to win.

"I had a [2021] goal to be top 200, actually! I don't know if I did this today, but that's my goal. 

"To play against a top-10 player is a great opportunity for me, and it's a great chance to show how I could play."

Pliskova, therefore, starts her year on a negative note, but there were no such problems for second seed Elina Svitolina, who was a 6-4 6-1 winner against Vera Zvonareva.

Last year's Australian Open finalist Garbine Muguruza cruised through with a 6-1 6-4 victory over Aliaksandra Sasnovich and sixth seed Elena Rybakina won in straight sets against Xiyu Wang.

Muguruza will face Maria Sakkari in an intriguing last-16 match next after the Greek ended the hopes of American Gauff with a comfortable 7-5 6-2 victory.

Top seed Sofia Kenin, who made two grand slam finals last year and won in Melbourne, will resume her campaign against Yulia Putintseva on Sunday.

Sofia Kenin and Coco Gauff both made it through to the second round of the Abu Dhabi Women's Tennis Open on a day of few shocks. 

Seven of the nine seeds in action on Thursday advanced, with only Marketa Vondrousova and Jennifer Brady falling by the wayside. 

Those upsets came despite Vondrousova and Brady each winning their opening sets - against Hsieh Su-wei and Tamara Zidansek respectively - the latter racing through 6-0 in the first before being reeled back in. 

Kenin and Gauff had no such problems, however. 

But top seed Kenin - the 2020 WTA Player of the Year - had to stay patient as she took down 789th-ranked Yang Zhaoxuan 7-6 (7-4) 6-2. 

The first set lasted more than an hour and saw Kenin face five break points, defending each of them, with another 11 Yang opportunities following in the second, although the world number four proved more clinical en route to victory. 

"It was the first match, obviously a bit of nerves, I had to find my groove," Kenin said afterwards. "Conditions weren't easy, it was quite windy.

"The first set was tough for me. I couldn't find the ball, I guess." 

Gauff was comfortable throughout, meanwhile, swatting aside Ulrikke Eikeri 6-0 6-1 to tee up a meeting with Maria Sakkari. 

Elina Svitolina, Karolina Pliskova and Aryna Sabalenka each also progressed in two sets, as did Garbine Muguruza, overcoming a potentially tricky hurdle in the form of Kristina Mladenovic. 

Muguruza was a 6-2 6-4 winner and afterwards said: "I was trying to do my game, dominating, not letting her dominate the point. 

"It's the first match of the year, it's a little bit tricky to get the feeling, but I'm happy with the win."