Novak Djokovic could not be happier with his form after coasting through his first two matches at the US Open.

The world number one, bidding to reach the final for a fifth straight year, had the easiest of afternoons in Arthur Ashe Stadium, defeating Paul-Henri Mathieu 6-1 6-3 6-0 in the second round.

As good as Djokovic was from the start, Mathieu was his own worst enemy, serving seven double faults in the opening set as he struggled to adjust to the windy conditions.

The Frenchman settled down in the second set and had a chance to break for 3-2 but could only watch as his forehand clipped the top of the net and dropped just wide.

Djokovic made him pay straight away with a break of his own and went on to take the second set, and the third was completely one-sided as he wrapped up victory after just an hour and 28 minutes.

The Wimbledon champion came into the tournament short on wins after a shaky start to the North American hard-court season but there has been no sign of weakness so far.

He said: "I wanted to get my job done as quick as possible. I don't feel like I need to play long matches to get into the groove. I feel that I'm hitting the ball very well.

"The second match was even better than the first one. Under the circumstances I think I came up with a very good performance.

"I stayed mentally tough and did not allow myself to get frustrated because of the wind and conditions that were obviously very tough for both of us."

The top seed next plays American Sam Querrey, who upset 28th seed Guillermo Garcia-Lopez 6-3 6-4 6-4.

Querrey's only win in eight previous meetings with Djokovic came at the Masters event in Paris two years ago.

He said: "I usually just worry about myself and try to focus on my game and not change up my strategy too much. I'll pretty much just try to serve big and be aggressive and take my chance with some big forehands."

Ninth seed Jo-Wilfried Tsonga eased to a 6-3 6-4 6-4 win over Aleksandr Nedovyesov, celebrating his win with some shadow boxing.

Tenth seed Kei Nishikori was two sets up when Pablo Andujar retired while American number one John Isner was untroubled in a 7-6 (7/5) 6-4 6-2 win over Jan-Lennard Struff.

The 13th seed now meets German Philipp Kohlschreiber, who has beaten him at the same stage of the US Open for the past two years.

"I wouldn't really call it a problem," said Isner. "I have beaten him more times than he's beaten me overall. But he's beaten me here.

"I thought our matches the last two years have been pretty high quality. I remember last year I wasn't disappointed with how I played. He just played better than me. Simple as that.

"In a few days' time I'm just going to have to try to be better than him."

There were mixed fortunes for the two teenagers left in the draw.

Australian 19-year-old Nick Kyrgios is making waves again and he moved through to the third round with a 6-4 7-6 (7/2) 6-4 victory over Andreas Seppi.

Kyrgios had come within one code violation of being defaulted in his first-round match but there was no need for him to get hot under the collar this time.

It was the end of the road, however, for 17-year-old qualifier Borna Coric.

Last year's junior champion had posted his first grand slam victory in round one with a thumping win over Lukas Rosol but ran out of steam against Victor Estrella Burgos.

The 7-6 (7/2) 4-6 6-4 6-2 win was a fantastic moment for 34-year-old Estrella Burgos, who also enjoyed his first slam victory on Tuesday.

He once again received vociferous support from the Dominican Republic ex-pat community and will meet fifth seed Milos Raonic next.

Estrella Burgos could not hold the tears back at the best moment of his career.

He said: "I had a big emotion when I was serving for the match, serving at match point. I cannot believe I'm in this situation. I'm going to make the third round at the US Open.

"I was a little nervous and it was very, very emotional for me. But thank God I got the point."

Estrella Burgos turned professional in 2002 but stopped to become a coach before deciding to give the tour another go in 2006.

It has taken him a long time to get to the top level, and he thought about retiring last year when he was out with an elbow injury.

Instead he came back and has climbed the rankings rapidly, reaching a high of 79, which will be surpassed when the standings are updated after the US Open.

"People from Dominica, I think they are partying now," he said. "They are very happy. This is very special for me, to come from a very, very long way down.

"I didn't have any idea when I was 18 years old about this tournament. But now I'm enjoying it so much. It doesn't matter if I'm 38, whatever, it makes me strong."

Raonic lost a set to German qualifier Peter Gojowczyk but recovered to win 7-6 (7/4) 5-7 6-4 7-6 (7/3) while Tommy Robredo completed yet another comeback from two sets to love down, this time against Simone Bolelli, and will meet Kyrgios in round three.

Robredo's win featured controversy at the end of the third set when Bolelli stopped playing after hearing a call of 'out' from the crowd, mistaking it for a line judge.

Referee Pascal Maria initially called for the point to be replayed but after a long discussion at the net it eventually stood, bringing up a set point which Robredo took to start his fightback.