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.
Rybakina continues clay winning streak with victory over Bronzetti
In-form Elena Rybakina has moved into the last 32 of the Madrid Open after a straight sets victory over Italian Lucia Bronzetti.
Number four seed Rybakina triumphed 6-4 6-3 on Friday and will next face either Marta Kostyuk or Mayar Sherif.
Rybakina was broken early in each set but ultimately had few problems getting over the line, converting four of her five break points to continue an impressive run of results after winning the Stuttgart Open last week.
She has now won five consecutive WTA matches and has 13 straight wins on clay courts to her name in a superb streak that started one year ago.
Data Debrief: Rybakina in elite company
Since the start of 2020, only two other players have claimed as many 13 consecutive WTA wins on clay, and they are Iga Swiatek and Simona Halep, so Rybakina is in elite company.
Rybakina's last defeat on this surface came in the 2023 edition of the Madrid Open, when she fell to Anna Kalinskaya in her first match, so this win represented a better start to her campaign in the Spanish capital.
Foden: De Bruyne the best in the Premier League
Phil Foden hailed Manchester City team-mate Kevin De Bruyne as the Premier League's best player after the pair both netted in the 4-0 win over Brighton and Hove Albion.
De Bruyne opened the scoring in Thursday's contest at Amex Stadium before Foden took over with a couple of goals of his own before half-time.
Julian Alvarez rounded off the scoring just after the hour in a one-sided contest as an Erling Haaland-less City moved to within a point of leaders Arsenal with a game in hand.
Belgium international De Bruyne now has four goals and six assists in just 13 league appearances for City this season.
Speaking to Sky Sports News after the win over Brighton, Foden said: "I think when he is at it, he is the best player in the Premier League."
Foden's first goal came via a deflected free-kick that he himself won, although replays showed he slipped rather than being fouled.
The England international doubled his personal tally with a composed finish after Brighton were caught in possession at the back.
Asked about playing more centrally, Foden said: "I have always said that I see myself there. This year I have moved inside and it has helped me massively.
"I enjoy it in the middle. It's where I want to be. At the moment, I am just enjoying my football and playing with freedom."
De Bruyne had earlier opened the scoring with a brilliant opener - his first headed goal for City in the Premier League - as City made it 30 games unbeaten in normal time across all competitions.
Alvarez then went on to round off the scoring in a game that not only saw the reigning champions close the gap on Arsenal, but also narrow the goal difference margin to eight.
"It was a good game," De Bruyne said. "I think we played really good in the first half and every game is a lot of pressure. All we can do is prepare as we did today and win the game that is in front of us.
"We just want to win game-by-game and push for the title. We don't get ahead of ourselves. Now the next game is coming quickly. Try to recover and we go again."
Kyle Walker assisted the De Bruyne and Alvarez goals - the first time the defender has set up two goals in a single Premier League game in what was his 390th appearance in the competition.
Reflecting on his rare headed goal, De Bruyne said: "It doesn't happen too much. Kyle gave a good cross and I think the only way I could reach it is by jumping to it. I will take it but it's not something I am good at."
City have rather ominously won four Premier League games in a row and travel to strugglers Nottingham Forest next up at the weekend, knowing victory in their remaining five games will secure an unprecedented fourth straight title.
"I trust my team. All respect to Liverpool and Arsenal, they are amazing," De Bruyne added. "Arsenal are doing what they need to do and we are also needing to do it. Work hard and be humble enough to keep pushing."
World number one Swiatek sees off Xiyu in Madrid opener
World number one Iga Swiatek overcame Wang Xiyu with the minimum of fuss on Thursday to progress to the third round of the Madrid Open.
Swiatek has yet to win the title in Madrid, which is the only clay-court European event at which the Pole has not triumphed, but she got off to a flying start with a 6-1 6-4 victory over Xiyu.
"I love this place. I got to know the city a little better last year," Swiatek said. "So this time I feel more comfortable around."
Next up for the 22-year-old is a third-round tie against 27th seed Sorana Cirstea on Saturday.
Data Debrief
Swiatek has registered 150 match wins on the WTA Tour since the start of 2022. Elena Rybakina and Coco Gauff are the next best with 108 wins each.
She also became the first player born this century to claim 50 combined match wins in Madrid, Rome and Roland-Garros, since the inaugural women's singles event at the Madrid Open in 2009.
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