The four-time Grand Slam champion overcame unseeded American Alex Michelsen 7-5, 7-6 (7/4) in a tightly contested encounter lasting one hour and 41 minutes at Hard Rock Stadium.
Despite being ranked 40th in the world, Michelsen pushed Sinner throughout, even surging to a 5-2 lead in the second set after capitalising on a break of serve while also contending with difficult sunlight conditions.
Sinner’s composure proved decisive. After creating three break points earlier in the opening set, he struck in the 11th game to seize control.
In the second set, he clawed his way back to force a tiebreak before sealing victory with a powerful serve.
“I feel like I served very well in important moments and that helped me out, especially in the tough moments,” said Sinner.
“But today was not easy — I played a night match yesterday and today in the daytime, so the conditions were very different.”
Awaiting Sinner in the last eight is 19th seed Frances Tiafoe, who progressed with a hard-fought 6-4, 1-6, 6-4 win over Terence Atmane.
Elsewhere, Spanish qualifier Martin Landaluce continued his breakout tournament. The 20-year-old, ranked 151st, stunned 32nd seed Sebastian Korda 2-6, 7-6 (8/6), 6-4, saving a match point in the second set.
Remarkably, Landaluce had not recorded a tour-level win in 2026 prior to this event, but has now also defeated 14th seed Karen Khachanov.
