Russia’s Daniil Medvedev shook off a leg injury to reach his first Grand Slam semi-final Tuesday at the US Open by defeating three-time major winner Stan Wawrinka while Roger Federer eyed his 46th Grand Slam semi-final berth.

Fifth seed Medvedev’s 7-6 (8/6), 6-3, 3-6, 6-1 triumph sent him into a Friday matchup against the later winner between Bulgaria’s 78th-ranked Grigor Dimitrov and 38-year-old Federer, owner of a record 20 Grand Slam titles.

“I feel really strange about this match but I’m really happy to be in my first semi-final,” Medvedev said.

Medvedev struggled with a sore left quadriceps muscle that made him consider quitting the match in the first set.

“Before the match, I was feeling perfect. In the first set I think I pulled my quadriceps,” Medvedev said.

“I had a really big pain in my quadriceps and thought I wasn’t going to continue the match.”

Medvedev took a medical timeout and had the area taped and took a painkiller.

“In the fourth set, I started feeling the painkiller and started moving better,” he said. “For sure, I hope to be ready for the semis.”

Medvedev, at 23, becomes the youngest US Open semi-finalist since Novak Djokovic in 2010 and Russia’s first Slam semi-finalist since Mikhail Youzhny at the 2010 US Open.

Swiss third seed Federer, who has a record 45 Slam semi-final visits, hopes to become the oldest Slam semi-finalist since Jimmy Connors at age 39 at the 1991 US Open.

Wawrinka, foiled in a bid for his second US Open title in four seasons, said he did not think Medvedev would be holding the trophy on Sunday.

“He can, but I don’t think he will. I think it’s going to be really difficult,” Wawrinka said. “Because he looks to start to be tired, and he has to beat some more tougher player in the semi-final, Roger or Grigor, and then in the final.

“But again, he’s showing last few weeks that anything can happen with him, so for sure he’s going to have a shot. He just need two more matches.”

Medvedev has maintained momentum from a sizzling August in which he reached three ATP finals, winning a title at Cincinnati and finishing runner-up in Montreal and Washington.

Boos greeted Medvedev as he walked onto the court at Arthur Ashe Stadium, the frosty reception stemming from his obscene gesture in a third-round match and subsequent taunts about how the jeers provide him inspiration to win, although he later called himself “an idiot” and needed to conduct himself better on court.

After the match he used the words “electric” for the atmosphere and “controversy” to describe his odd relationship with US Open fans, who gave him mixed applause and boos.

“What I have done is not so good, still people support me... What can I say. I like to be myself, guys.

“I have to say, sorry guys, and thank you.”

No rhythm

Medvedev broke Wawrinka to open the match but, after the medical timeout, he was broken in the 10th game to set up the tie-break. Medvedev led 5-2, lost the next four points, then took the last three, claiming the first set on a service winner.

The Russian rode a break in the fourth game to capture the second set but two double faults helped Wawrinka break in the second game of the third set and the Swiss fought off four break points in the ninth game to hold and force a fourth set.

Medvedev broke at love for a 2-0 lead and cruised from there to victory in two hours 34 minutes.

“I never really found the right rhythm,” Wawrinka said. “I wasn’t at my best today. I wasn’t moving great. I didn’t mix enough my game, and at the end it was a struggle.”

Federer, chasing his sixth US Open title but first since 2008, could become the oldest Open Era (since 1968) Slam finalist since Ken Rosewall, 39, at the 1974 US Open and potentially the oldest-ever Open Era Grand Slam champion.

Dimitrov would be the lowest-ranked Slam semi-finalist since 94th-rated Rainer Schuettler at Wimbledon in 2008 and the lowest-ranked US Open semi-finalist since 174th-rated Connors in 1991.

Other quarter-finals Wednesday send Spanish second seed Rafael Nadal, an 18-time Grand Slam champion, against Argentine 20th seed Diego Schwartzman and French 13th seed Gael Monfils against Italian 24th seed Matteo Berrettini.