Rafael Nadal overcame a spirited challenge from Kazakhstan's Andrey Golubev to reach the second round of the US Open at Flushing Meadows this morning.

The Spaniard was made to work hard before clinching a 6-3, 7-6, 7-5 victory against a player ranked 98th in the world and who only recently ended an 18-match losing streak on the ATP World Tour.

Nadal, who will meet Frenchman Nicolas Mahut in the second round, said: "I was practising very well all week. For sure I was nervous. That's normal. It's normal to start the tournament like this with some nerves.

"And what happened today, he didn't help because he played very fast all the time. All the shots, he was trying to hit a winner on almost every shot. So it was difficult for me to find the rhythm.

"But it's a positive start winning in straight sets, even if it was unbeliev-able that I won in straight sets.

"I'm happy for the victory. I'm happy to come back to New York. I think I didn't play that bad. But the mental part was positive tonight. The tennis for sure can improve. I have to play a little bit more inside the court. But I am confident I can do it."

Top seed Novak Djokovic barely had to break sweat to make it to the second round as Irishman Conor Niland retired through illness while trailing 6-0, 5-1 at the Arthur Ashe Stadium.

Niland had required attention early in the second set after apparently being ill during the warm-up, and although he soldiered on for a short while, he bowed to the inevitable as Djokovic proved far too strong.

Niland looked lost for most of the match as Djokovic swiftly got back to winning ways after losing his last appearance – against Andy Murray when he suffered a shoulder injury in the final in Cincinnati a week ago – for only his second defeat of an incredible season.

After completing a 6-0 whitewash in the opening set, Djokovic took the first game of the second, too, before Niland finally made a breakthrough, levelling it at 1-1 to earn a few cheers.

But soon after he was receiving attention from medics and although he battled on, it was clear he did not have anything like what it would take to trouble Djokovic and the illness forced him out.

David Ferrer and Jo-Wilfried Tsonga had little trouble reaching the second round, but last year's semi-finalist Mikhail Youzhny was beaten in straight sets by Ernests Gulbis.