That moment when you realize all hope is lost and you reach for the ripcord. Not that Jo-Wilfried Tsonga didn’t have a legitimate injury. He called for medical treatment between the second and third sets Tuesday night on Arthur Ashe Stadium Court and got a wrap for a left knee that has bothered him in the past.

But he was down two sets to world No. 1 Novak Djokovic, who was playing lights-out tennis. So when Tsonga missed a serve to open the third set, he looked plaintively at the referee and tapped out of his seemingly inevitable straight-set loss while trailing 6-3, 6-2 to the tune of some mild booing.

“It’s already tough to play against one of the best tennis players, but when I don’t have my knee, I have no chance to come back from two sets to love,” Tsonga admitted. “So for me, it’s important to save what I can save.”

It shaped up as a tough quarterfinal U.S. open match because Tsonga came in with six wins in 21 meetings with Djokovic. Instead it became the third match out of five in which Djokovic watched as his opponent retired.

Djokovic graciously claimed he sensed something was wrong with Tsonga midway through the second set when he began “upholding his first serve.”

The U.S. Open is the last of the season’s Grand Slam events, but it’s gradually turning into a cakewalk for Djokovic, who advanced to face Frenchman Gaels Monfils in the semifinals Friday. “This Grand Slam is very unique for me,” Djokovic said. “I never experienced something like this to have three retirements on the road to the semifinals.”

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It was hard to blame Tsonga for making a quick exit. Everything he hit over the net came back low, hard and out of reach. The brilliance of Djokovic was on display in the second set when he broke for a 2-1 lead. On the second deuce point, Djokovic sent a forehand screaming crosscourt with Tsonga stuck on the other side. On the next point, Djokovic zipped a backhand crosscourt the other direction with the same result. Tsonga netted a forehand on break point.

Asked if he’s worried about his match toughness approaching the semifinals, Djokovic said he’ll gladly trade that for freshness. “In this stage of the season, considering some physical issues I have had in the last month and a half, this was the scenario that I needed and wished for,” Djokovic said. “I’m feeling very close to the peak. That’s where I want to be.”