World number one Jannik Sinner will face Daniil Medvedev in the Shanghai Masters quarter-finals after both had straight-set victories on Wednesday.

Sinner put some old demons to rest in overcoming American Ben Shelton 6-4, 7-6 (7/1), while Medvedev took out Greece's Stefanos Tsitsipas 7-6 (7/3), 6-3.

Shelton, ranked 16, knocked Sinner out at the same stage last year, but on Wednesday the Italian looked confident from the start as he won in 88 minutes.

The US Open champion pulled ahead in the ninth game of the first set, breaking when Shelton hit long, then dominated the second set tiebreak.

"It was very tough, you don't have so much control when you play against him... I just tried to stay strong mentally," said Sinner.

World number five Medvedev and Tsitsipas were meeting for the 14th time.

The Greek started the second set strongly, breaking in the first game, but Medvedev broke in the fourth and eighth to progress.

Medvedev and Sinner have met four times this year already in the final stages of tournaments.

Sinner beat Medvedev in the semi-finals at Miami, the quarter-finals at the US Open and in the Australian Open final, but the Russian ended the Italian's hopes in the last eight at Wimbledon in an epic five-set battle.

"I'm gonna bring the fight," said Medvedev.

"I could have done much better in the US Open... I didn't explore enough my potential during this match. So I'm going to try to explore this potential tomorrow," he added.

Also through to the quarterfinals is world number two Carlos Alcaraz, who beat Sinner in the China Open final a week ago.

The 21-year-old was facing off against veteran Gael Monfils, winning 6-4, 7-5 for a 12th straight victory.

The 38-year-old Frenchman had upset Alcaraz at their last meeting in August at Cincinnati, and the Spaniard admitted that "was on his mind" during the match.

"I'm just really, really happy I won the match, and that I stayed calm through the whole match," he said.

"Playing against Gael is never easy... You need to be focused on every ball," he added.

Also in action on Wednesday are four-time Shanghai champion Novak Djokovic and world number three Alexander Zverev. (AFP)