LONDON — Jannik Sinner felt ill. He was dizzy. Hadn’t slept well the night before. Wimbledon’s top-seeded man, who recently attained the No. 1 ranking, definitely did not want to quit playing against Daniil Medvedev in the quarterfinals, but things were not looking good.

Sinner was treated by a trainer and left the court during the third set Tuesday, then briefly surged before faltering again down the stretch, eventually losing to a more-aggressive-than-usual Daniil Medvedev 6-7 (7), 6-4, 7-6 (4), 2-6, 6-3.

“I was struggling physically,” said Sinner, who had won his last five matches against Medvedev, including a five-setter in the final of the Australian Open in January. “It was not an easy moment. I tried to fight with that what I had today.”

It wasn’t enough.

Not against the crafty Medvedev, the 2021 U.S. Open champion who will face Carlos Alcaraz in the semifinals at the All England Club for a second consecutive year.

“Was a bit up-and-down match, in a way, from both sides,” Medvedev said.

Alcaraz, the defending champion and No. 3 seed, took a bit of time to get going in his quarterfinal, but once he did, there was no stopping him during a 5-7, 6-4, 6-2, 6-2 victory over No. 12 Tommy Paul at No. 1 Court.

“We try just to find solutions,” said Alcaraz, coming off a title at the French Open last

month and seeking his fourth Grand Slam trophy. “For me, obviously, it’s going to be really difficult to play my best tennis every match.”

Over at Centre Court, it was not immediately clear what was wrong with Sinner, who leaned back in his sideline chair, rested his head in a hand and had his heart rate checked before heading to the locker room. During a later changeover, Sinner draped a towel over his head.

While he did regain his usual verve, particularly on his booming forehand, and pushed the match to a fifth set — the 36th this fortnight and the most at any Grand Slam tournament in the Open era, which dates to 1968 — Sinner could not get over the line.

Even though he won more points (164-160), accumulated more winners (61-56), made fewer unforced errors (49-45), hit more aces (17-15) and finished with far fewer double faults (11-4).

“It’s a tough one to swallow,” Sinner said.

Medvedev, a 28-year-old from Russia, began playing closer to the baseline than he often does. He found the space to deliver more winners, compiling 13 in the closing set alone, broke for a 3-1 lead in the fifth, and was on his way back to the semifinals.

“Today,” Medvedev said, “a lot of tactical things worked well.”

After eliminating the 22-year-old Sinner, Medvedev now goes up against the 21-year-old Alcaraz, back-to-back tests against the two new young stars of men’s tennis.

Against Paul, Alcaraz raised his level after a so-so opening set, putting together a 26-12 advantage in winners over the last three.

“When he starts building energy and building momentum … it feels a little bit different than most of the other guys,” Paul said. “He can play some seriously amazing, amazing tennis.”

In the women’s quarterfinals, Donna Vekic reached the final four at a major for the first time in her 43rd Slam, defeating qualifier Lulu Sun 5-7, 6-4, 6-1, and French Open runner-up Jasmine Paolini eliminated No. 19 Emma Navarro 6-2, 6-1 in less than an hour.

Navarro got past four-time major champion Naomi Osaka and reigning U.S. Open champ Coco Gauff earlier in the tournament.

Sinner was a Wimbledon semifinalist a year ago and carried a nine-match winning streak into Tuesday.

His exit follows that of the No. 1 women’s seed, Iga Swiatek, in the third round. It is the first time since 2018 that both the top woman and top man are gone from Wimbledon before the semifinals. That year, Roger Federer lost in the quarterfinals, and Simona Halep in the third round.