World number one Sinner and seven-time champion Djokovic remain on course for a mouthwatering semi-final clash but the top seed’s match on Centre Court was overshadowed by Dimitrov’s heartbreak.
The Italian was staring at the exit door trailing 3-6, 5-7, 2-2 before the Bulgarian 19th seed pulled up holding his right pectoral muscle and was unable to continue.
Sinner rushed to his aid but his 34-year-old opponent was barely able to wave to acknowledge the crowd’s warm ovation.
“Honestly I don’t know what to say,” said Sinner. “He is an incredible player, I think we all saw this today.”
“He’s been so unlucky in the past couple of years. An incredible player, a good friend of mine also. We understand each other very well off the court too,” he added. “Seeing him in this position, honestly, if there would be a chance that he could play the next round, he would deserve it.”
The injury-prone Dimitrov has now been forced to retire in each of his past five Grand Slam appearances.
Sinner himself suffered a nasty fall in the opening game of the fourth-round clash and appeared to be suffering discomfort in his right elbow.
The three-time Grand Slam champion had been in regal form in the first three rounds at the All England Club, dropping just 17 games.
Sinner, who is due to face American 10th seed Ben Shelton in the quarter-finals, said he would be having an MRI scan on Tuesday to assess the extent of the damage to his elbow.
Shelton beat Italy’s Lorenzo Sonego in four sets.
Earlier, sixth seed Djokovic endured a nightmare start to his match against Australian 11th seed Alex de Minaur but battled back to win 1-6, 6-4, 6-4, 6-4.
Fresh from his 100th win at Wimbledon on Saturday, making him the third player to achieve that feat after Martina Navratilova and Roger Federer, Djokovic reached his 16th quarter-final at the tournament.
Aged 38, the Serb is aiming to win a record 25th major title, breaking a tie with the long-retired Margaret Court, and to equal Federer’s record of eight men’s crowns at the All England Club.
That would make him the oldest Grand Slam singles champion in the Open era.
Djokovic’s 101st victory at Wimbledon came under the gaze of the Swiss great, who was sitting in the front row of the royal box alongside his wife Mirka.
“It’s probably the first time he’s watching me and I’ve won the match,” he said. “The last couple I lost, so good to break the curse.
“No, it’s great, obviously, great to have Roger, a huge champion and someone that I admired and respected a lot. “We shared the stage for so many years, and it’s great to have him back.”
In the last eight, Djokovic faces Italian 22nd seed Flavio Cobolli, who beat former Wimbledon runner-up Marin Cilic 6-4, 6-4, 6-7 (4/7), 7-6 (7/3).
In the women’s draw, Iga Swiatek coninued her serene progress with a 6-4, 6-1 rout of Danish 23rd seed Clara Tauson.
Swiatek, fourth in the rankings, is a five-time Grand Slam winner but has never made a Wimbledon semi-final.
The 24-year-old is in a strong position in the second week of the tournament after the exit of so many of the top seeds.
“Honestly it’s pretty amazing. It’s the first time I really enjoyed London, sorry guys,” Swiatek said, referring to her previous Wimbledon woes. “We are tennis players, so we feel well off the court when we feel well on the court.”
The Polish player next faces Russian 19th seed Liudmila Samsonova, who beat Spain’s Jessica Bouzas Maneiro 7-5, 7-5. (AFP)