Sinner and Pegula advance to third round at Miami Open
The 24-year-old Italian and reigning Wimbledon champion dispatched 76th-ranked Damir Dzumhur of Bosnia and Herzegovina 6-3, 6-3 on the Florida hardcourts.
"First round matches are never easy, so I'm very happy and let's see what's coming," Sinner said.
He will next face either France's 31st-ranked Corentin Moutet or Czech Tomas Machac.
Four-time Grand Slam winner Sinner, who won the 2024 Miami crown, captured his 25th career ATP title by beating Daniil Medvedev in the Indian Wells final earlier this month.
Sinner is trying to become the first man to sweep the "Sunshine Double" by winning at Miami and Indian Wells since Roger Federer in 2017.
Sinner broke for 2-0 lead when Dzumhur sent a backhand long and the Italian held serve from there to take the first set in 34 minutes, saving a break point in the seventh game with an ace.
In the second set, Sinner broke for a 2-1 lead and broke again on match point with a backhand winner to end matters after 70 minutes, dropping only eight points on his serve in the match.
"Starting off with a break straight away, I tried to be a bit aggressive," Sinner said. "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 a while."
On the women's side, US fifth seed Jessica Pegula advanced to the third round in only 38 minutes after Britain's Francesca Jones retired due to illness trailing 6-1, 3-0.
"I was just trying to focus on myself, stay in there every point, stay super positive," Pegula said.
Pegula, last year's Miami runner-up, will next face Canadian 26th seed Leylah Fernandez, who eliminated fellow left-hander Oksana Selekhmeteva 7-6 (7/1), 3-6, 6-1 in two hours and 25 minutes.