Djokovic battles through in New York

Defending champion Novak Djokovic was made to work hard for his victory over Jerzy Janowicz in the US Open first round.

Djokovic has been struggling with a wrist injury for some time and required a medical time out during the first set at Arthur Ashe Stadium.

He battled on but never looked comfortable as he defeated Janowicz 6-3 5-7 6-2 6-1 to progress to the second round and the world number one is hopeful he will improve as the tournament goes on.

"It's getting better and better each day. I'm glad that I'm experiencing that so hopefully, as the tournament progresses, I'll reach my peak," Djokovic said.

"Calling for the medical time-out was just prevention. It's all good. To be honest, I take it day by day. That's what I feel at the moment.

"It's good, as I said, just to finish the match. I'm pleased that as the match progressed, I was feeling better and better.

"Tomorrow is a new day. I hope that I'll feel good overall, so I'm able to perform at my best for the next match."

Djokovic will face Jiri Vesely in the second round.

There were no such problems for Rafael Nadal as the Spaniard opened up his tournament with a straight sets win over Denis Istomin.

Nadal missed the French Open and Wimbledon because of a wrist injury but he never looked to be in danger of an early exit, defeating Istomin 6-1 6-4 6-2.

"I am hitting very well in the backhand, but it's true that I need time with the forehand," Nadal said.

"I need confidence and I need to keep practicing the forehand. It's not easy to go two-and-a-half months out of competition in the middle of the season without hitting a forehand.

"I need to have the confidence again with my wrist. That is coming, because I feel the wrist much better, and every day feel that the wrist is a little bit better.

"That's a very important thing for me. The most important thing."

Elsewhere, 2014 champion Marin Cilic overcame Rogerio Dutra Silva 6-4 7-5 6-1, while Britain's Kyle Edmund shocked Richard Gasquet 6-2 6-2 6-3.

In the women's tournament, third seed Garbine Muguruza avoided an upset by coming from one set down to defeat Belgian Elise Mertens 2-6 6-0 6-3.

Meanwhile, Australian Open champion Angelique Kerber did not drop a game as she booked her place in the second round.

Kerber was leading Polona Hercog 6-0 1-0 when her Slovakian opponent was forced to call it a day due to leg cramps.

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