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Sinner lost the top ranking after surrendering his U.S. Open crown to the Spaniard this month but has responded well to the setback in Beijing, claiming a seventh semi-final spot in the eight tournaments he has played this year.

The world number two clinched the opening set in 26 minutes thanks to big hitting from the baseline but faced stiffer resistance in the second and had to dust himself off after falling awkwardly in the eighth game.

He then found himself a break down at 4-5 but hit back immediately to deny Marozsan the set.

Sinner held and pounced on his opponent's serve again in the 12th game, sealing his 40th tour-level match win of a season in which he served a short doping ban.

"I feel like I started off very well in the first set. We both played well in the second set. I had some break chances at 4-3, I couldn't use them," Sinner said.

"He's someone whose peak is high, which I knew before the match. When he was serving for the set he made a couple unforced errors which helped me to come back and win in two."

Up next for the four-times major champion is Australian third seed Alex De Minaur, who reached the semis when Czech 20 year-old Jakub Mensik retired from their match with a left leg injury while trailing 1-4 in the opening set.

American teenager Learner Tien reached his first ATP Tour semi-final after fourth seed Lorenzo Musetti retired trailing 4-6 6-3 3-0. The Italian appeared to be hampered by a thigh or groin issue.

Eighth seed Daniil Medvedev eased past German second seed Alexander Zverev 6-3 6-3. The Russian has beaten Zverev 14 times in 20 meetings, including eight of their past 10 matches.