A fearless Andrey Rublev outfoxed Roger Federer 6-3 6-4 in the third round of the Cincinnati Masters on Thursday, but Novak Djokovic has progressed to the quarter-finals.
The Russian qualifier broke the third-seeded Swiss in his first two service games and won 81 per cent 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.
Federer has won the tournament more than anyone, using it as a springboard to the US Open.
He had 16 unforced errors against the 70th-ranked Rublev, who raised both fists and wiped a teary eye in celebration after Federer's forehand sailed long to end it.
Struggling with his serve, Federer got broken twice in the first set.
"And there you have it. It set the tone for the match a little bit," Federer said. "He was super clean - offense, defense, serving well. He didn't give me anything."
But Federer, who lost a classic five-set match for the Wimbledon title to Djokovic, still thinks he's in good shape heading into the US Open despite the upset in Cincinnati.
World No.1 Djokovic reached the last eight with a 6-3 6-4 win over Pablo Carreno Busta.
"All in all, it was a very good, quality match," Djokovic said. "I'm pleased I'm going in the right direction and looking forward to the next one."