NEW YORK -- If there were any boos directed Jannik Sinner's way at the US Open, they were imperceptible amid the polite applause from the sparse crowd at Arthur Ashe Stadium when he was introduced Tuesday before the No. 1-ranked man's first match since his doping case emerged a week ago.

After a sloppy and slow opening set, Sinner pulled away for a 2-6, 6-2, 6-1, 6-2 victory against Mackenzie McDonald of the United States to reach the second round at Flushing Meadows.

There were no apparent signs in the stands or disparaging shouts making reference to what no one knew about for months: Sinner tested positive twice for trace amounts of the anabolic steroid clostebol in an eight-day span in March.

Nothing was announced publicly until last week, when word came that the 23-year-old Italian was docked prize money and ranking points from the tournament where the first result appeared, but he escaped a suspension because it was ruled he was not at fault and the drug entered his system unintentionally, through a massage from his physiotherapist.

In his first public comments on the matter, at a pre-tournament news conference Friday, Sinner said he had fired the fitness trainer who bought an over-the-counter spray containing clostebol in Italy and the physiotherapist who used it for a cut on his finger before treating the player and transferring the substance to his body.

During a brief on-court interview in Ashe, Sinner wasn't asked about the case, which has drawn some criticism from other players, including Novak Djokovic, about the way it was handled and questions about whether certain athletes are treated differently than others when it comes to the process for determining punishments related to doping.

But in an indication of the way the crowd treated him, Sinner offered this observation: "The support is always amazing, so thank [you] everyone for coming, for staying."

Against McDonald, an American ranked 140th who fell to 4-13 in 2024, Sinner was way off the mark at the outset. He double-faulted. He put what should have been an easy smash into the net. He messed up volleys. It added up to 14 unforced errors in the initial set, helping McDonald grab five games in a row from 2-all to collect that set and go up a break in the second.

"I started a little bit not in the best way. But for sure, the first matches in every tournament, they're not easy. ... I tried to stay there mentally and get in a rhythm," Sinner said. "I will try to improve for the next match. For sure, I have room to improve."

That one will come against another American foe, Alex Michelsen.

Sinner turned things around quickly in the second set Tuesday, making just 15 unforced errors combined over the last three sets, including zero in the third.

It's the sort of play everyone is used to seeing from him, particularly on hard courts like those used in New York. He improved to 29-2 on the surface this season with four titles, including his first Grand Slam trophy at the Australian Open in January.