The Russian qualifier broke the third seeded Swiss in his first two service games and won 81% of his first serve points to wrap up the upset in just over an hour.
The 21-year-old shed tears of joy after pulling off the biggest win of his career.
“It is such an amazing feeling when you’re playing a legend like Roger and all these people supporting him until the end,” he told ESPN in an on-court interview.
“One day I hope I’m going to feel the same.
“Today I was just trying to do my best and was thinking in my head that I need to play every point until the end no matter what.”
The win sets up an all-Russian quarter-final with ninth seed Daniil Medvedev.
Barty and Sakkari to meet after marathon wins
On the women’s side, top seed Ash Barty overcame 49 unforced errors and a stiff challenge from Anett Kontaveit to reach the quarter-finals with a 4-6 7-5 7-5 win the same day.
On a day of epic three-set battles, French Open champion Barty needed more than two hours to tame her Estonian rival, rifling a forehand winner on match point.
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Aug 15, 2019; Mason, OH, USA; Ashleigh Barty (AUS) returns a shot against Anett Kontaveit (EST) during the Western and Southern Open tennis tournament at Lindner Family Tennis Center. Mandatory Credit: Aaron Doster-USA TODAY Sports
Barty set up a meeting with Maria Sakkari, who needed even longer to dispatch Aryna Sabalenka 6-7(4) 6-4 6-4 on a hot and humid day.
The Hawk-Eye review system played a key roll in Barty’s win when the Australian, trailing 5-4 and 30-15 in the third set, challenged a serve from Kontaveit that had been called in.
The system showed the ball was slightly long, denying Kontaveit what would have been two match points. Barty went on to win the next three games to seal the victory.
An in form Sakkari battled back to dispatch ninth seed Sabalenka on the Ohio hardcourts.
Sakkari saw five set points slip away in the first set but the Greek continued to fight and got help from Sabalenka, who double faulted 17 times and needed a trainer apply ice to her right ankle late in the match.
Venus Williams also went the distance before claiming a 2-6 6-3 6-3 victory over Croatia’s Donna Vekic.
The 39-year-old Williams has struggled at times this season but has been resilient in Cincinnati, defeating defending champion Kiki Bertens in three sets in the previous round.
The seven-times Grand Slam champion will have her work cut out in the next round when she faces either Wimbledon champion Simona Halep or big-serving American Madison Keys.
