Ash Barty crashed out of the Adelaide International at her first hurdle after going down in straight sets to Danielle Collins.
It took only 65 minutes for American Collins to defeat the defending champion and world number one in a 6-3 6-4 triumph.
Barty, who had a bye in the first round, did have opportunities, breaking in the first game of the match and building a 4-1 lead in the second set.
But on both occasions Collins stormed back, claiming her first win in four attempts against home favourite Barty, who had beaten her in the semi-finals of last year's tournament.
Coco Gauff continued her fine run to reach a first WTA quarter-final since August 2020 with an impressive comeback win over sixth seed Petra Martic.
The American triumphed 5-7 6-3 6-4 in two hours and 12 minutes to book a clash with compatriot Shelby Rogers at the WTA 500 event.
Gauff did not relinquish serve once after losing the first set and did not even offer up a break-point chance in the decider, which she sealed with a pivotal early break secured with a passing winner.
"I go into every tournament thinking that I can win," said the 16-year-old.
"Obviously that's impossible, to have a perfect record, but I go into every tournament believing that I can win.
"I try not to think far ahead in the match, at least I just try to focus on my next match, just because you have to get through that before you can get to the finals, and just take it one match at a time."
Second seed Belinda Bencic will face Storm Sanders in the quarter-finals after a 6-1 6-3 win over Misaki Doi.
In a match where she was not quite as dominant as the scoreline suggests, Bencic had to fend off 12 break points but was successful in saving 10 of them.
Number four seed Elise Mertens withdrew before her match with a shoulder injury, so Anastasija Sevastova beat lucky loser Christina McHale to set up a last-eight tie with Jil Teichmann.
Osaka crashes out of Libema Open, De Minaur through to semi-finals
Naomi Osaka crashed out of the Libema Open despite fighting to a tie-break in the final set, with Bianca Andreescu progressing to the semi-finals after a 6-4, 3-6, 7-6 (7-3) win.
Osaka's match was interrupted by rain early on with her in the lead, but Andreescu came back out in top form to take the first set.
The Japanese raced through the second though, taking a 5-0 lead before holding off Andreescu's fightback to go into a decider.
Despite an impressive comeback to force a tie-break in the final set, Osaka became sloppy, with her mistakes contributing to the Canadian's path into the semi-final, where she will face Dalma Galfi.
Elsewhere, Alex de Minaur is through to the semi-finals after a comfortable straight-sets victory over Milos Raonic.
Despite a long break due to bad weather, the Australian eased into the next round with a 7-5, 6-2 victory on Friday.
He will face either Ugo Humbert or Gijs Brouwer in the next round.
Data Debrief: Osaka not close enough, De Minaur in cruise control
Despite winning more points (98 compared to 94), and winning more games (16 to 15), Osaka could not hold her nerve in the tie-break to reach the semi-finals.
Competing as the top seed for the first time in his tour-level career, De Minaur felt no pressure as he rallied in the second set to ensure Raonic would not find a way back into the match, winning his last five games in a row on his way to victory.
Federer hopes Djokovic, Nadal and Murray 'can keep playing forever'
Roger Federer expressed his hopes for former rivals Novak Djokovic, Rafael Nadal and Andy Murray to "keep playing forever", insisting the ATP Tour is "better with them".
Federer called time on his glittering career in 2022, while the other three - who between them formed tennis' 'big four' - appear not to be far away from joining him in retirement.
Nadal, who will miss Wimbledon to focus on his "last Olympics", and Murray are expected to hang up their racquets this year, with the latter revealing in February that he does not "plan on playing much past this summer".
Meanwhile, 24-time major winner Djokovic is also likely be absent from the grass-court major, having undergone knee surgery following his withdrawal from the French Open last week.
Now in their late 30s, all three players are certainly at the twilight of their remarkable careers.
But Federer, who says the quartet all now "get on super well" after years of rivalry, hopes they are not finished just yet.
"I really don't think there are any words of advice that I can give him," he told BBC Sport. "Retirement is so deeply personal. When you take that decision, everybody is in a completely different circumstance.
"We've gone through similar things, but I'm too far away to give advice. If [Andy] called me up, I'd be happy to answer some questions. He's had this massive hip issue and what he is doing is inspirational.
"I hope Andy, like Rafa and Novak, can keep playing forever, like a fan. The tour is better with them. I was watching Roland-Garros last week, and I was like: 'Wow, they're so good - I used to do that too!'
"It's tricky sometimes and there’s definitely moments when you don't like a certain opponent, but then you like him so much. It's important to remember this as a player - it is just tennis and, in the end, we can be normal.
"You see us being super friendly with each other after the rivalry, and we get on super well."
Afghanistan advance to Super 8s and seal New Zealand elimination
Afghanistan booked their place in the T20 World Cup Super 8s with a seven-wicket victory over Papua New Guinea, while eliminating New Zealand from the competition.
Rashid Khan's side claimed a third successive win to maintain their perfect start in Group C, which they top ahead of co-hosts West Indies with a superior net run-rate.
Afghanistan chose to bowl and made a fast start in San Fernando, dismissing captain Assad Vala, Lega Siaka and Sese Bau within four balls to leave the Barramundis at 12-3 early in the third over.
Wicketkeeper Kiplin Doriga top-scored with 27, before they were bowled out for 95.
Their opponents were also steady out of the blocks, having been reduced to 22-2 inside the third over.
However, Gulbadin Naib's unbeaten 49 from 36 balls - featuring four fours and two sixes - steadied the ship, while his unbroken stand of 46 with Mohammed Nabi helped get Afghanistan comfortably over the line.
Data Debrief: Farooqi leads the charge to condemn Black Caps to early exit
Fazalhaq Farooqi (3-16) led from Afghanistan's field again, with the tournament's leading wicket taker increasing his tally to 12 from three innings.
The side note to their victory was the sealing of New Zealand's fate with a match to spare.
Runners-up in 2021 and semi-finalists in the last three tournaments, it is the first time the Black Caps have failed to advance beyond the first group stage at the T20 World Cup.
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