MIAMI (AFP) — World No. 2 Jannik Sinner made a smooth start Saturday at the Miami Open, where defending champion Jakub Mensik shook off a "horrible" first set to win his opening match.

Six days after he lifted the Indian Wells trophy, Sinner launched his pursuit of "Sunshine Double" in confident style with a 6-3, 6-3 victory over 76th-ranked Damir Dzumhur.

"First-round matches are never easy," the 24-year-old Italian, who won the 2024 Miami crown, said.

After beating Daniil Medvedev for his first Indian Wells title, Sinner is trying to become the first to sweep the Indian Wells and Miami ATP Masters 1000 titles since Roger Federer in 2017.

He pocketed the first set against Dzumhur in 34 minutes and broke the Bosnian for a 2-1 lead in the second set before breaking again on match point with a backhand winner.

"Starting off with a break straight away, I tried to be a bit aggressive," said Sinner, who dropped just eight points on his serve.

"At times it worked very well, at times I made a couple of unforced errors. But I didn't have a lot of time to adjust here. It's very different than in Indian Wells."

Former No. 1 Medvedev also had little time to adjust, but he managed to fight back for a 6-7 (10/12), 6-3, 6-1 victory over 19-year-old Japanese wildcard Rei Sakamoto.

Mensik, who fell in the third round at Indian Wells, was feeling the after-effects of illness as well as the pressure of defending his title in a rocky first set, but righted the ship to beat Australian Adam Walton 3-6, 6-2, 6-4.

"The first set, it was horrible from my side," the Czech said.

After surrendering his serve twice in the first set, Mensik regrouped to break Walton in the opening game of the second set on the way to forcing a third, and with a break in hand for a 3-1 lead, rolled home.

"It was really difficult to come back to the match rhythm," Mensik said.

"(I'm) really happy that mentally I stayed focused and tough. The pressure that was around, I tried not to focus on that, tried to focus on my game."

Fourth-seeded German Alexander Zverev cruised into the third round with a 6-2, 6-4 victory over 133rd-ranked American Martin Damm. But eighth-seeded home hope Ben Shelton was ousted by Kazakhstan's Alexander Shevchenko 6-7 (3/7), 7-6 (7/3), 6-3.

Fourth-seeded Coco Gauff led the way into the women's fourth round, roaring back for a 3-6, 6-0, 6-1 victory over fellow American Alycia Parks.

Teenagers Mirra Andreeva and Victoria Mboko booked a last-16 meeting that will be their third clash of the WTA season.

Eighth-seeded Russian Andreeva defeated Czech Marie Bouzkova 7-6 (7/4), 6-2, while 10th-seeded Canadian Mboko downed Russian qualifier Anastasia Zakharova 6-1, 7-5.

Andreeva, 18, and 19-year-old Mboko have split their last two matches, Andreeva winning in the final at Adelaide in January before Mboko sent her packing in the third round at Doha — saving a match point in the three-set win and going on to reach the final.