Keys beats Swiatek in big Cincinnati upset, Kvitova ousts Jabeur
Swiatek, who won her 50th match of the year in the previous round, saved four match points but was far from her best as she again exited a second tournament in the U.S. swing at the last-16 stage after last week's Canadian Open.
Keys, Cincinnati champion in 2019, had never taken a set off Poland's Swiatek in two previous meetings but the American was far more clinical with her powerful returns and groundstrokes, breaking the world number one five times.
"I obviously had a couple of games with a couple of match points, but I'm just so happy to be able to get the win," Keys said after her first career win over a world number one.
"The last time I played her she beat me pretty badly, so I'm pretty glad to get that one under my belt."
Swiatek had complained about the tennis balls used in the women's game in the US tournaments being different to the men's, and against Keys the top seed made several unforced errors and was broken twice in the opening set.
A toilet break between sets did little to help Swiatek regain her composure as Keys put herself firmly in the driving seat as she raced to a 5-0 lead in the second set.
Serving to stay in the match, Swiatek saved two match points and that inspired her to win the next four games as Keys made several errors.
But it only delayed the inevitable as Keys broke Swiatek to clinch victory with a forehand winner.
US Open champion Emma Raducanu - who had beaten former Grand Slam champions Serena Williams and Victoria Azarenka in the previous two rounds - was brought down to earth with a bump in a 7-5 6-4 defeat by Jessica Pegula, the highest-ranked American at eighth in the world.
"I definitely felt like I was pretty nervous tonight, not really knowing - well, knowing how she plays but not actually practising or hitting with her," Pegula said.
"And then playing at night, the conditions are heavier. Just seemed so different when I got out there. I'm happy with how I pulled through with that and I guess another quarter-final."
Keys will next face Wimbledon champion Elena Rybakina (23), who beat Alison Riske-Amritraj (32) 6-2 6-4 to sail into the quarter-finals.
Wimbledon runner-up and fifth seed Ons Jabeur (27) was knocked out by Czech Petra Kvitova (32) 6-1 4-6 6-0.
Jabeur served poorly in the opening set with four double faults but the Tunisian put up a brave fight in the second to take the match to a decider.
However, Jabeur wilted in the blazing sunshine and although she saved two match points, Kvitova secured her place in the last eight.
Kvitova next faces Australian Ajla Tomljanovic, who staged a stunning comeback to beat Russian Veronika Kudermetova 3-6 7-6(4) 6-3 and reach her first WTA 1000 quarter-final.
"The restaurant is still open and I'm going to get five Graeter's ice creams," said Tomljanovic, who was backing up after finishing her previous match at 1.30 a.m. local time on Thursday.
World number two Anett Kontaveit looked to have taken charge of her tie against Zhang Shuai when she won the opening set at a canter but her Chinese opponent dug deep to claim a stunning 2-6 6-4 6-4 upset.
Last year's U.S. Open semi-finalist Aryna Sabalenka defeated Shelby Rogers 6-4 6-7(2) 6-4, sealing victory with a backhand winner down the line.
"It was a crazy match, she played unbelievable tennis," said Sabalenka, who faces Zhang in the next round.
