Carlos Alcaraz rallied from a set down and held his nerve in a deciding tiebreak to beat defending champion Jannik Sinner 6-7(6) 6-4 7-6(3) in the China Open final on Wednesday and win his fourth title of the season.

French Open and Wimbledon champion Alcaraz, who won both of his previous meetings with Sinner this year, recovered from a slow start to wrap up victory in three hours, 21 minutes and improve his head-to-head record with the Italian to 6-4.

Sinner and Alcaraz pushed each other to the limit in the latest chapter of the burgeoning rivalry that has taken the ATP Tour by storm.

"He could have won in two, I could have won in two, it was a really close match. Jannik once again showed that he's the best player in the world, with the level that he's playing," Alcaraz, 21, said.

"It is unbelievable, it's a really high quality of tennis, physically, mentally, he's a beast."

After both players defended break points in a cagey start, Alcaraz seized the early break for a 3-1 lead when Sinner's backhand went wide, before consolidating the advantage in the next as his Italian opponent netted a shot.

World number one Sinner, whose last win over Alcaraz came in the semi-finals of this tournament last year, gradually found his range to level at 5-5 and save two set points in the tiebreak to clinch the first set.

Alcaraz was on the ropes early in the second set and Sinner pushed him hard in a 15-minute game, but the second seed successfully held serve for 4-4.

Sinner's failure to break in the lengthy game appeared to take the wind out of his sails, as Alcaraz sped through the next two games to level the match at a set apiece.

The Spaniard cranked up the intensity on his forehand and broke for a 2-1 lead in the third set, but with victory seemingly in sight, he suffered a lapse in concentration and allowed Sinner to level at 4-4.

In the deciding tiebreak, Sinner snatched control to take a 3-0 lead, but some excellent work at the net helped Alcaraz edge a couple of rallies and go ahead 4-3, before finally clinching the title with an emphatic cross-court forehand winner.

The result denied Australian Open and US Open champion Sinner becoming the first man to retain the crown at the China National Tennis Centre since Novak Djokovic won four straight titles between 2012-15. (Reuters)