Naomi Osaka was a major casualty at the Western & Southern Open after the four-time grand slam champion was stunned by unseeded opponent Jil Teichmann.
Osaka was expected to book her spot in the quarter-finals of the WTA 1,000 tournament but crashed out in three sets on Thursday.
It was a different story for world number one, Ash Barty, who blitzed defending champion, Victoria Azarenka en route to the quarters in Cincinnati.
Osaka looked on track for a routine win after racing out to a 3-0 lead before closing out the first set.
The Japanese star was clawed back by unheralded wildcard Teichmann 3-6 6-3 6-3.
Teichmann claimed the biggest win of her career after rallying past Osaka, who lost for just the fourth time when winning the first set since 2017 – a record which was 118-3.
“I thought she played really well. I thought in the first set I was doing everything I was supposed to do.
“Then in the second set I feel like, and also in the third set I felt like I was a bit too defensive maybe,” Osaka said.
“I felt like I learned a lot from this match today, and I felt that, if anything to take away from this, I tried my best throughout the entire match, so I can sleep at night.”
Olympic gold medallist, Belinda Bencic awaits Teichmann in an all-Swiss affair after the 10th seed led 7-5 2-1 when Karolina Muchova retired hurt.
It was a merciless display from top seed Barty, who eased past two-time grand slam winner Azarenka 6-0 6-2.
Thursday was the heaviest loss that Azarenka has had to stomach since 2007, when as a 17-year-old she suffered 6-1 6-1 defeats to Romina Oprandi at Amelia Island and to Karin Knapp at the French Open.
“Vika [Azarenka] has this way of bringing out the very best in me. I’ve enjoyed playing on the same side as her in doubles.
“We’ve had success in doubles, we’re great mates, and we have a lot of respect for each other,” said Wimbledon champion Barty.
“For both of us that means we always have really good battles and regardless of who wins and who loses you always get a good handshake, you look each other in the eye and you say ‘Too good’, and it’s like it never happened.
“That’s what I really respect about Vika. I knew today was going to be exceptionally tough and I feel like I played a great match throughout the whole thing.”
Next for Barty is a clash with ninth seed Barbora Krejcikova – who edged out former world number one Garbine Muguruza 6-1 6-7 (5-7) 6-2.
There were also victories for three-time slam winner Angelique Kerber and two-time major champion Petra Kvitova as they prepare to meet in the last eight.
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