Australian Open champion Aryna Sabalenka lost for the first time in 14 matches, and Coco Gauff set up a semi-final clash with Iga Swiatek at the Dubai Tennis Championships on Thursday.
Sabalenka fought back from a set down to end the title defence of Jelena Ostapenko a day earlier, but she came up short against Barbora Krejcikova as her Czech opponent overcame a tough first set to run out a 0-6 7-6 (7-2) 6-1 victor.
Sabalenka, playing in her first event since claiming a maiden grand slam title in Melbourne, romped into the lead by breaking Krejcikova's serve three times to go a set ahead.
But the world number two was pegged back in the second as Krejcikova battled to force a tie-break, which she dominated to level the match.
Krejcikova then completed the shock victory in style, breaking the second seed twice in the final set before clinching the win on her third match point to end Sabalenka's run of 13 straight triumphs.
Karolina Muchova's withdrawal due to an abdominal injury means it is Jessica Pegula who will face Krejcikova in the semi-finals on Friday.
After Swiatek reached the final four by virtue of Karolina Pliskova pulling out because of an illness, Gauff set up a sixth meeting with the world number one by beating Madison Keys 6-2 7-5.
In those five previous clashes between the pair, Gauff is yet to win a set.
But after cruising past Keys, doing so by converting four of five break points and winning 90 per cent of her service games, Gauff is confident of improving her dismal record against Swiatek on Friday.
"All five times, I did something wrong," Gauff said. "To be honest, she's playing great tennis and there's a reason she's world number one.
"Tomorrow I have no pressure. I just have to play my game. I definitely think I've gotten better since the last time I played her.
"Ranking is just a number at the end of the day. You just have to step on the court believing you can win, and that's what I'm going to do tomorrow."
Medvedev pushed all the way to avoid third-round scare in Italian Open
Daniil Medvedev had to dig deep to overcome Hamad Medjedovic at the Italian Open on Monday and stay in with a chance of retaining his title.
Medvedev came out on top with a 7-6 (7-5), 2-6, 7-5 victory, but was made to work hard to avoid a third-round upset.
After enduring an up-and-down opening two sets in which he hit 10 double faults, Medvedev rallied into a lead before holding off Medjedovic’s fight-back.
The second seed remained composed to break in the match’s final game to advance after two hours and 50 minutes.
Medvedev will now play Tommy Paul in the next round on Tuesday, with the American seeing off Dominik Koepfer 6-4, 6-3.
Data Debrief: Reigning champion fights on
Medvedev has reached the last 16 at all 5 Masters 1000 events this season, with only Alexander Zverev able to match that distinction.
It was not an easy ride for him though, as Medjedovic wanted to prove a point against his first Top 10 opponent in what was his first Masters 1000 third round.
Swiatek passes Kerber test to reach Italian Open quarter-finals
Two-time Italian Open champion Iga Swiatek advanced to the quarter-finals of this year's tournament with an impressive 7-5 6-3 win over Angelique Kerber on Monday.
Three-time grand slam winner Kerber provided Swiatek with a real step up after routine victories over Bernarda Pera and Yulia Putintseva in the first two rounds on the clay in Rome.
Kerber responded to Swiatek's first break – which came in the eighth game – with one of her own, but the world number one then recaptured her composure to force a series of break points in Kerber's next two service games, finally converting at the eighth attempt to take the opener.
Kerber refused to go away, breaking straight back in the first game of the second set, but Swiatek upped her game to take the contest away from the 36-year-old.
Swiatek dropped just three further points on her own serve from there, adding three breaks of her own to set up a last-eight meeting with Madison Keys for Tuesday.
Data Debrief: Swiatek unmatched on clay
While Kerber rolled back the years to trouble Swiatek early on, she lacked the staying power to live with the world number one in longer rallies on a surface where she is truly unmatched.
Her win ratio at clay-court events at WTA 1000-level now stands at 88.2 per cent (30 wins, four defeats), the best of any player to have played a minimum of five matches since the format's 2009 introduction, ahead of Serena Williams at 88 per cent.
Osaka sees encouraging Italian Open run halted by Zheng in last 16
Naomi Osaka's promising Italian Open run was halted by Zheng Qinwen on Monday, as the seventh seed denied the four-time grand slam champion a quarter-final place.
Following Saturday's triumph over Daria Kasatkina – her second successive straight-sets win over a top-20 opponent in Rome – Osaka laughed off the "Clayomi" moniker given to her by some fans.
On Monday, her old troubles on the surface came back to the fore as Zheng dominated from the off to make the tournament's last eight for a second straight year, winning 6-2 6-4.
Osaka saw her serve broken in the very first game only to hit straight back, but Zheng assumed control by taking seven straight games to go from 2-1 down in the opener to 2-0 up in the second set.
The 21-year-old produced a clinical performance and converted all four of her break points, winning 78 per cent of first-serve points to Osaka's 68 per cent as she teed up a quarter-final clash with either Coco Gauff or Paula Badosa.
Data Debrief: 'Clayomi' no more as Zheng triumphs
Osaka impressed on a surface long regarded as her worst in Italy, but it was a bridge too far for her on Monday, Zheng reaching her fourth WTA 1000 quarter-final.
Since the format's introduction in 2009, she is just the second Asian player to reach multiple quarter-finals on both hardcourts and clay at that level before the age of 23, the other being Osaka.
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