World number two 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 tennis' "Sunshine Double" in confident style with a 6-3, 6-3 victory over 76th-ranked Damir Dzumhur.

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

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 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 number one 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.

Medvedev needed two hours and four minutes to subdue Sakamoto, who was playing only his seventh tour-level match and facing his first top-10 opponent.

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."

Andreeva-Mboko rematch

The women's fourth round began to take shape, with teenagers Mirra Andreeva and Victoria Mboko lining up 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.

Alexandra Eala, whose surprise semi-final run last year launched her rise from 140th in the world to her current 29th, reached the last 16 with a 6-3, 7-6 (7/2) victory over Poland's Magda Linette -- who had toppled third-ranked compatriot Iga Swiatek in the second round.

Women's second-round play also continued as the rain-hit tournament got back on schedule.

Fifth-seeded American Jessica Pegula, runner up to Aryna Sabalenka last year, advanced when ailing British opponent Francesca Jones retired while trailing 6-1, 3-0 in their match.

Australian qualifier Talia Gibson -- coming off an impressive quarter-final run in Indian wells -- took down four-time Grand Slam champion Naomi Osaka of Japan 7-5, 6-4.

Gibson next faces 18-year-old American 18th seed Iva Jovic, who eliminated former world number two Paula Badosa of Spain 6-2, 6-1.