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(CNN) —  

There has been a massive, unexpected development at the US Open: The “Big 3” in the men’s singles draw is down to one.

An ailing No. 3 Roger Federer was stunned by Grigor Dimitrov, with the unseeded Bulgarian advancing to the semifinals 3-6, 6-4, 3-6, 6-4, 6-2.

It’s the first time Dimitrov, 28, has beaten Federer in eight tries. He’ll next face the fifth-ranked Daniil Medvedev, who defeated No. 23 seed Stan Wawrinka earlier Tuesday. Dimitrov and Medvedev have split their two previous matches, back in 2017. Neither have reached a grand slam final.

Grigor Dimitrov beat Roger Federer in the quarterfinals of the US Open.
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Grigor Dimitrov beat Roger Federer in the quarterfinals of the US Open.

After the fourth set, Federer sought the trainer and left the court for a medical timeout, a rarity coming from him. His level dropped in the fifth set.

“I just needed some treatment on my upper – what is it – back, neck,” Federer told reporters. “Just needed to try to loosen it up, crack it and see if it was going to be better.

“Yeah, but this is Grigor’s moment and not my body’s moment, so… it’s OK.”

The exit of the 38-year-old Swiss follows world No. 1 Novak Djokovic; the 32-year-old Serb retired in his match in the round of 16 against Wawrinka on Sunday because of shoulder trouble.

The lone member of the Big 3 left? That would be 18-time grand slam champion No. 2 Rafael Nadal, who is in the other half of the draw. The Spaniard, 33, continues to chase Federer, who leads the all-time men’s list with 20 major titles, and to try and distance himself from Djokovic, who has 16.

Nadal faces No. 20 seed Diego Schwartzman of Argentina – whom he is 7-0 against – on Wednesday in the quarterfinals.

Federer joins Novak Djokovic with his US Open exit.
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Federer joins Novak Djokovic with his US Open exit.

’I fought with what I had’

This was not vintage Fed on Tuesday night. He looked off balance, misfiring on his shots and spraying errors. And Federer had an injury concern of his own.

Federer said the trouble in the affected area started Tuesday afternoon.

“I was able to play,” he said. “It’s OK. It’s how it goes. I tried my best. By far not too bad to give up or anything. Grigor was able to put me away. I fought with what I had. That’s it. So it’s OK.”

Federer was asked of his tournament plans for the rest of the year.

“I guess Laver Cup, Shanghai, Basel, maybe Paris, London,” he said. “That’s the schedule for now. I don’t know if the team have other ideas or not. I’m happy to get a bit of a break now, go back to practice, reassess and attack from there.”

The last time Federer lost in five sets came in July in the final of Wimbledon, when he lost to Djokovic despite having two match points on his serve.

That loss did not cross his mind on Tuesday, he said.

“I know people read into it,” Federer said. “They think, all that stuff. That is definitely not the reason why I lost tonight. I was ready to go, try my best. It wasn’t enough. It’s purely here tonight.”

Federer hasn’t won the US Open since 2008.

’Clearly in the end he was not at his best’

Meanwhile, Dimitrov, aside from seven double faults, played the cleaner match, taking advantage of a hobbled Federer late.

“Clearly in the end he was not at his best,” Dimitrov said. “I used every opportunity I had.”

Up until this point, it had been a lackluster year for Dimitrov, having gone 1-7 in his last eight matches entering the US Open. Previously ranked as high as No. 3 in the world in 2017, Dimitrov currently is 78th – his lowest ranking since he was 87th on June 4, 2012.

Dimitrov is the lowest-ranked grand slam semifinalist since No. 94 Rainer Schuettler at Wimbledon in 2008 and the lowest-ranked US Open semifinalist since Jimmy Connors at No. 174 in 1991.

This will be the Bulgarian’s third career major semifinal, having also reached this stage at the Australian Open in 2017 and Wimbledon in 2014.

“I think the past six, seven months have been pretty rough for me,” Dimitrov said. “But I had somebody to lean on, my friends, my family. I kept on believing again in the work, the rehab I had to put behind my shoulder, the exercise, the practice, fixing up the racket a little bit. There were so many things I had to adjust in such a small but big period of time.

“Next thing you know, you’re almost end of the year, you have a result like that. It’s pretty special to me.”