New York, Aug 30 (AFP) Defending champion Novak Djokovic overcame an arm injury scare and long-time rival Rafael Nadal shone in 33-degree heat as the US Open showcased its $650 million upgrade on Monday.
World number one Djokovic, also the 2011 winner in New York and chasing his third major of the year, defeated Jerzy Janowicz of Poland 6-3, 5-7, 6-2, 6-1.
Nadal, the 2010 and 2013 champion and seeded to face Djokovic in the semi-finals, eased to a 6-1, 6-4, 6-2 win over Denis Istomin of Uzbekistan.
In the women's event, second seeded Angelique Kerber, the Australian Open champion, needed just 33 minutes to progress but Roland Garros winner Garbine Muguruza required three sets and a visit from the doctor before she survived.
Djokovic had admitted that he was "not 100 percent" after suffering a wrist injury on the eve of the Olympics where he was a first-round loser.
But it was the upper right arm that bothered the Serb on Monday night as he played his first Grand Slam match since his shock third round exit at Wimbledon.
The 29-year-old needed treatment after just five games of the first set but eventually pulled through against Janowicz who had played just two matches all year due to a knee injury.
"It was hard to follow Phil Collins," joked Djokovic in reference to the lengthy opening ceremony which featured the veteran English rocker under the new $150 million roof on Arthur Ashe Stadium.
On his arm injury, Djokovic added: "It's never easy to play at this level throughout the year. There are periods where you aren't 100 percent."
Djokovic next faces Jiri Vesely, the Czech who knocked him out of Monte Carlo this year.
Nadal's reward for a fifth win in five meetings with Istomin is a match-up with Italian veteran Andreas Seppi.
A wrist injury forced the Spaniard into an early retirement at the French Open and sidelined him from Wimbledon before a gold medal run in the doubles at the Olympics helped ease his misery.
"The most important thing is that I am here in New York. Injuries are part of the career. I had a hard time this year," said the fourth seed.
Canadian fifth seed Milos Raonic, the runner-up to Andy Murray at Wimbledon, overcame German dangerman Dustin Brown 7-5, 6-4, 6-4.