Two-times former champion Novak Djokovic overcame a lapse in concentration to beat unseeded American Tennys Sandgren 6-1 6-3 6-7 6-2 and reach the third round of the US Open on Thursday.
Djokovic, who was also pushed to four sets in punishing daytime temperatures above 90 Fahrenheit (32C) in the first round, was far more comfortable in the evening at the Arthur Ashe Stadium, breaking early and running away with the opening set in 31 minutes.
"I thought I played really well in the first two sets and then I lost it mentally," the Serb said courtside. "I lost my composure and concentration but I got it back in the fourth."
Djokovic also spoke about the noise from the crowd both between and during points but said it had not been a factor in him losing concentration.
"I was just referring to the atmosphere that the night session at the US Open has," the sixth seed told reporters.
"I've played many times here. It has no connection to my loss of concentration. It was just me, being me sometimes, the other me that my first me doesn't like.
"You just have to accept it. You can't expect that 23,000 people are quiet. Wimbledon is all white, it's tradition. You can't hear a sound when you play a point. Here it's different. That's why these majors are unique in their own way."
The Serb, who won Wimbledon this year, will face 26th seed Richard Gasquet of France in the third round.
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Tennis is back on Sky Sports screens with the Laver Cup in September while we will also have coverage of the ATP Finals in November with every match live on Sky Sports. But first, we will be across the final major of the year in New York as the US Open right through to the final with live blogs, reports, features and reaction.