Djokovic was off the pace in a lackluster first set against three-times Grand Slam champion Wawrinka but seemed to right the ship in the second when he took a 4-1 lead. "Imagine having to retire due to pain at the Grand Slam and after everything you brought to tennis and still will, you are being booed", another person added.
Earlier Sunday, Ash Barty was knocked out by Wang Qiang, leaving only one of this year's major champions in the women's tournament.
Federer lost the opening set in each of his first two matches for the first time in his 19 US Open appearances, but the No. 3 seed has been pretty ideal since while playing the first match of the day in Arthur Ashe Stadium.
His next opponent is Grigor Dimitrov of Bulgaria, who defeated Alex de Minaur of Australia 7-5, 6-3, 6-4.
Wawrinka has battled almost two years to recover Slam-winning form after knee surgery and his performance, after a French Open quarter-final run, shows his journey is almost complete.
Roger Federer has gotten his groove back.
He also had been 11-0 in fourth-rounders at Flushing Meadows.
Federer, who dropped the first set in each of his first two matches, hasn't dropped a set since. Federer closed out the match after a 20-stroke rally with an emphatic backhand victor down the line.
Three-time grand slam champion Wawrinka understands how Medvedev can feed off negative energy, saying: "For sure I understand how you can get from any atmosphere". Despite 38 Grand Slam wins between them, the two storied rivals have, remarkably, never faced each other at the U.S. Open. The difference, she said, was she couldn't control points against Osaka, but she and McNally did that.
Coco Gauff's singles run was ended Saturday by No. 1 Naomi Osaka, but Gauff is still rolling in doubles.
His bid for a fourth U.S. Open championship and 17th Slam trophy in all suddenly dissipated at the conclusion of what for him amounted to a listless and ineffective effort. "I feel sorry for Novak".
They meet Sunday for the first time since Wawrinka's victory in the 2016 U.S. Open final, with a trip to the quarterfinals going to the victor. The 2019 season was the first in which Federer has played the French Open since 2015 and he has only featured in 10 tournaments all year.
It was a unusual way for Djokovic's title defence to end.
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