Top seeds Aryna Sabalenka and Alexander Zverev crashed out of the Cincinnati Masters in a matter of hours on a rainy Wednesday of fourth-round action.
American Tommy Paul saved a match point on the way to a 4-6, 7-6 (8/6), 6-4 upset of Germany's Zverev.
But the biggest shock came on the women's side where Czech Sara Bejlek, ranked 35th, stunned world No 1 Sabalenka 7-6 (9/7), 6-4 in a gritty match that finished up shortly after the clock ticked past midnight into Thursday morning.
Former champion Sabalenka led by a break in the opening set and was up 5-1 in the tiebreaker before Bejlek roared back to pocket the set in 65 minutes.
Bejlek broke the Belarusian three times in the second set, rallying from 4-1 down and securing the win with a love game capped by an ace.
"I lost my words – it feels incredible," Bejlek said after her first win over a top-10 player.
"I was playing what I was feeling and not really thinking. I was trying not to be nervous and just play. I believed in myself no matter what."
Bejlek, who won the Abu Dhabi hard court title in February as a qualifier, booked a quarterfinal clash with American Madison Keys.
It was yet another setback for Sabalenka as the start of the US Open looms on August 30.
The four-time Grand Slam champion was ousted in the fourth round of the Toronto Masters last week, having lost in the same round at Wimbledon and in the quarterfinals at Roland Garros.
Zverev's match was interrupted by rain for 90 minutes in the seventh game of the second set and had two more five-minute pauses as drops were dried from the court.
French Open champion Zverev had a chance to close it out at 6-5 in the second-set tiebreaker but stuffed a volley into the net.
The German again gained an edge in the deciding set with a break for 4-2, but Paul broke back in the next game and again for a 5-4 lead on the way to his third win over Zverev in their last four meetings.
"I'm not sure how I did it," Paul said. "I put some returns in, he gave me some looks at second serves and he threw in a few doubles (faults). That always helps a ton.
"I went after the ball a bit more, I was having fun out there."
Second seed Felix Auger-Aliassime of Canada was another casualty, falling 6-3, 6-4 to American Frances Tiafoe.
Zverev's conqueror Paul next faces Roland Garros runner-up Flavio Cobolli, who labored two and a half hours to engineer a turnaround against red-hot Spaniard Rafael Jodar 4-6, 7-6 (7/3), 6-3.
American sixth seed Taylor Fritz dispatched Australian Chris O'Connell 6-4, 6-3.
Thiago Tirante, who upset Novak Djokovic in the second round, continued his surprise run, reaching his first Masters quarterfinal with a 5-7, 6-4, 6-4 victory over Jakub Mensik.
Australian Alex de Minaur was no match for Frenchman Arthur Fils, who cruised to a 6-3, 6-4 victory over the fifth seed.
GAUFF ADVANCES
The women's 2023 champion Coco Gauff saved all eight break points she faced in a 6-3, 6-2 win over Czech Marie Bouzkova.
The fourth seed double-faulted on her first match point but leapt up to smash an overhead winner on her second chance.
"I played well the whole match, going for my shots, coming forward and not letting her counter-punch," Gauff said. "I'm happy with how I played."
Defending women's champion Iga Swiatek needed four match points to get past Diane Parry of France 6-3, 6-3.
The seventh-seeded Pole now faces a re-run of last week's Toronto final against Elena Rybakina, who beat Diana Shnaider 6-4, 6-4.
Six-time Grand Slam champion Swiatek captured her first title of 2026 with her victory over reigning Australian Open champion Rybakina in Toronto.
Two other current Grand Slam champions bowed out.
Ukraine's Marta Kostyuk rallied from a set down to beat French Open winner Mirra Andreeva 4-6, 6-0, 6-2.
Wimbledon champion Linda Noskova fell to Amanda Anisimova 6-1, 6-4 in another weather-disrupted match.