The 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as the favourite to take a record-extending fifth title in the Chinese financial hub, with other top seeds already withdrawn or knocked out.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 like he might not be able to continue when the match went to a decider, but 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, breaking in the fourth game, but shortly afterwards had to take a medical break when his left ankle slid out behind him as he rushed towards the net.

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 briefly again during a break in play in the second set, and looked increasingly fatigued, crouching over frequently in between rallies.

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

An agonised Djokovic dropped to the floor and remained splayed out on court with his chest heaving, as his team rushed over.

But he picked himself up and in the third set had an incredible revival, breaking in the first and seventh games and sending the stadium into a frenzy.

Djokovic is the highest-ranking player left in the competition.

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 event in Shanghai has been beset by injuries, as players have battled temperatures of over 30 Celsius and humidity levels peaking at over 80 percent.

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.

Zizou Bergs and Gabriel Diallo took it down to the wire in their match, with the Belgian eventually prevailing in a prolonged third set tiebreak 3-6, 7-5, 7-6 (10/8).