LONDON - Top seed Jannik Sinner struggled with an elbow problem and was given an almighty scare before advancing to the quarterfinals of Wimbledon after a cruel twist of fate for his 19th-seeded opponent Grigor Dimitrov who retired injured at two sets up.

Novak Djokovic continued his quest for Grand Slam glory at the All England Club with a battling victory over Alex de Minaur while five-times major champion Iga Swiatek found her grasscourt wings to fly past Clara Tauson.

The drama was reserved for the evening clash on Centre Court as Dimitrov, who had pulled out injured in his last four majors, played exquisite tennis to go up 6-3 7-5 2-2 but then crashed to the ground after a big ace to hold serve.

Sinner, who had been hampered for much of the contest by a right elbow issue after slipping and falling to the turf early on, was left feeling sorry for his opponent who threw in the towel after a short assessment by a doctor.

"I don't know what to say because he's an incredible player. I think we all saw this today," said Sinner, who was by a tearful Dimitrov's side while the Bulgarian was attended to.

"He's been so unlucky in the past couple of years. He's an incredible player, a good friend of mine also, and we understand each other very well off the court too.

"Seeing him in this position... if there would be a chance that he could play in the next round, he would deserve it. Now I hope he has a speedy recovery. Very, very unlucky from his side.

"I don't take this as a win at all... just an unfortunate moment to witness for all of us."

Sinner later told reporters he would have an MRI scan to check his own injury.

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"It happened very early in the match, first game. It was quite an unfortunate fall. We checked the videos a bit, and it didn't seem a tough one, but I still felt it quite a lot, especially serve and forehand," he added.

"So let's see... tomorrow we are going to check with MRI to see if there's something serious and then we try to adjust it."

Sinner next faces American 10th seed Ben Shelton, who beat another Italian in Lorenzo Sonego 3-6 6-1 7-6(1) 7-5 to advance to the quarterfinals at Wimbledon for the first time, as did Flavio Cobolli, who downed Marin Cilic 6-4 6-4 6-7(4) 7-6(3).

Rocky road

Djokovic marched into the Wimbledon last eight for the 16th time but the Serbian trod a rocky road before defeating De Minaur 1-6 6-4 6-4 6-4 to keep alive his quest for a 25th major title to surpass Margaret Court.

Watched from the Royal Box by another great in Roger Federer, the man whose record eight All England Club trophies Djokovic is trying to equal, the sixth seed surrendered the first set in 31 minutes before roaring back to win.

"We did catch up very shortly," Djokovic said of his meeting with Federer afterwards.

"We greeted each other. He congratulated me and said it was a great match. That's all. It was a very short greeting, but it was really nice to have him around.

"He's one of the greatest legends of our game. So it always is extra special when he's on the stands. I'm glad to break the curse and win in front of him. It's a big relief."

Federer's fellow Swiss and former doubles partner Belinda Bencic made her first Wimbledon quarterfinal in nine attempts after dismissing 18th-seeded Russian Ekaterina Alexandrova 7-6(4) 6-4 in a little under two hours on a breezy Court One.

The 28-year-old Tokyo 2020 Olympic champion shed tears of joy after she finally broke the fourth-round barrier 15 months since giving birth to her daughter Bella and she said she was surprised at her high level.

"I'm really happy about it. Of course, I try not to think about it. I feel great on the practice court. When I was coming back, that's why I felt like I came back earlier than expected, than I expected for myself," Bencic said.

"I'm also surprised about how fast the results are coming."

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She will need all her battling qualities when she takes on seventh seed Mirra Andreeva, the Russian teenager who made short work of American 10th seed Emma Navarro 6-2 6-3 on her Centre Court debut with her idol Federer still in attendance.

Swiatek shrugged off a slow start to beat Danish 23rd seed Tauson 6-4 6-1 and set up a meeting with Liudmila Samsonova, who saw off Jessica Bouzas Maneiro 7-5 7-5.