Italy's Sinner needed just an hour and 39 minutes to get past the 49th-ranked Michelsen, giving himself a match point with a crisp forehand winner down the line and polishing it off with a crosscourt forehand volley.

He'll next play Australian wild card Christopher O'Connell as he aims to stay on course for a semi-final showdown with Carlos Alcaraz, the 2022 US Open champion who won both the French Open and Wimbledon this year.

O'Connell advanced with a 6-3, 6-4, 3-6, 6-3 victory over Italian qualifier Mattia Bellucci.

"Very happy," said Sinner, who beat Michelsen in the second round of the Cincinnati Masters this month.

"He's a very tough opponent. We played each other in Cincinnati a week ago. I knew what to expect, he knew what to expect a little."

Sinner went on to claim his fifth title of the season in Cincinnati.

A day later it was revealed that Sinner had escaped a ban despite twice testing positive for an anabolic agent in March, authorities accepting his explanation that the result was the result of inadvertent contamination.

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