Jannik Sinner won the 21st title of his career by thrashing American teenager Learner Tien 6-2, 6-2 in the China Open tennis final on Wednesday.

The Italian world number two lifted the trophy for the second time on Beijing's hard courts, where he beat Daniil Medvedev in the final on his tournament debut in 2023.

The 24-year-old is the third man to win multiple China Open titles after Novak Djokovic with six and Rafael Nadal with two.

His only loss on Beijing's centre Diamond Court has been to great rival Carlos Alcaraz, who won last year's championship match in three gripping sets.

Alcaraz was not defending his title in the Chinese capital and on Tuesday won the Japan Open in Tokyo.

Sinner broke immediately in the first set on the way to outclassing the 19-year-old Tien, who was in his first ATP final.

The world no 52 got a rare chance to break in the second game of the second set but Sinner quickly retook control, ending a one-sided match with 10 aces over the one hour and 12 minute final.

Tien was never really in it, despite some flashes of his rich potential.

Sinner's win in Beijing marked his third title this season, after his victories at the Australian Open and Wimbledon.

Sinner may now have a chance to snatch back the top ranking in men's tennis before the season ends after Alcaraz pulled out of the Shanghai Masters injured on Tuesday.

The Spaniard took the world number one ranking from Sinner when he defeated the Italian in the US Open final.

Sinner is the top seed in Shanghai, which began this week. (AFP)