MIAMI - Jannik Sinner powered into the Miami Open quarter-finals on Tuesday, defeating unseeded American Alex Michelsen in straight sets to stay on course for the "Sunshine Double".
Italian second seed Sinner, who is bidding to follow up his triumph at Indian Wells with victory in Miami, bided his time before completing a 7-5, 7-6 (7/4) win in 1hr 41min.
The four-time Grand Slam champion, who will face 19th seed Frances Tiafoe in the last eight, was made to work hard by the 40th-ranked Michelsen.
After a cagey opening Sinner began to put pressure on Michelsen's serve in the ninth game of the first set, carving out three break points.
Michelsen rode out that storm, but Sinner finally broke through in the 11th game before serving out for the first set.
Michelsen hit back in the second set, breaking Sinner for a 4-2 lead before holding to go 5-2 up.
Michelsen appeared to struggle with the bright late afternoon sunlight on the Hard Rock Stadium's main court and Sinner came roaring back to force a tiebreak.
Sinner sealed the win with a thumping serve that Michelsen could only return wide.
"I feel like I served very well in important moments and that helped me out, especially in the tough moments," said Sinner, who unfurled 15 aces to Michelsen's three.
"But today was not easy -- I played a night match yesterday and today in the daytime, so the conditions were very different."
Home hope Tiafoe advanced to his quarter-final date with Sinner after battling past France's Terence Atmane 6-4, 1-6, 6-4.