San Francisco Frontiers - Djokovic vanquishes exhaustion to push through to Shanghai quarters

The hard-won victory keeps Djokovic on track as the favourite to take a record-extending fifth title in the Chinese financial hub, with other top seeds already withdrawn or knocked out.

The 38-year-old almost looked unable to continue when the match went to a decider, but he conjured up the energy to break his decade-younger opponent twice in the third set.

"Thank you, thank you everyone, I love you!" he shouted in Chinese to the adoring crowd before leaving court almost immediately after play finished.

The 24-time Grand Slam champion had a good start despite the 84 percent humidity, breaking Munar in the fourth game.

Djokovic's problems began shortly afterwards when his left ankle slid out behind him as he rushed towards the net, and he had to take a medical timeout.

He grimaced in pain as he was attended to by an on-court physio, but managed to resume to hold the fifth game.

Djokovic received treatment again in the second set, and looked increasingly fatigued, crouching over frequently in between rallies and throwing up on court.

Chinese fans waving Serbian flags roared in support, but 41st-ranked Munar ultimately broke in the 12th game of the second set after an unforced error from his opponent.

An agonised Djokovic dropped to the court and remained splayed out as a medic rushed over.

But he picked himself up for a compelling third-set revival, breaking in the first and seventh games and sending the stadium into a frenzy.

- Oldest quarterfinal player -

Djokovic is now the oldest player to reach an ATP Masters 1000 quarterfinal, and the highest-ranking player left in Shanghai.

World number one Carlos Alcaraz withdrew from the tournament to rest, and second, third and fourth-ranked Jannik Sinner, Alexander Zverev and Taylor Fritz have all been eliminated.

The Shanghai event has been beset by injuries, as players have battled the humidity coupled with temperatures over 30 degrees Celsius (86 Fahrenheit).

Sinner was forced to retire on Sunday after being seized with extreme cramps.

World number 11 Holger Rune, who has also struggled with the conditions, called on Tuesday for tennis authorities to bring in a heat policy for events like Shanghai.

The Dane is through to the last eight after he took out France's Giovanni Mpetshi Perricard 6-4, 6-7 (7/9), 6-3.

He will face qualifier Valentin Vacherot, who upset the Netherlands' Tallon Griekspoor 4-6, 7-6 (7/1), 6-4.

At 204th in the world, the Monegasque is the lowest-ranked player to ever make the Shanghai quarterfinals, the tournament said.

Djokovic will next face 44th-ranked Zizou Bergs.

The Belgian took Canada's Gabriel Diallo down to the wire, prevailing in a prolonged third set tiebreak 3-6, 7-5, 7-6 (10/8).

E.Cruz--SFF