The 2012 champion at Flushing Meadows, who comes into the final Grand Slam of the year low on form and seeded eighth, needed four sets to dispatch Robin Haase of The Netherlands.

It was 90 minutes into the match, at the start of the third set, that the problems began for the Briton.

"I was in a good position, and then my body failed me," Murray, who won the first two sets 6-3, 7-6(6), told BBC Sport.

"I panicked, because you don't know what to do.

"I got broken at the beginning of that third set, and you think: 'What do I do?

"Do I try to conserve energy or do I try to finish it in three sets?'

"I don't really know how I managed to get through."

The 27-year-old, who said he suffered from cramp in several parts of his body, lost the third set 6-1 and faced a shock first round defeat.

But despite his serve suffering considerably, Murray was still able to rally to a fourth set 7-5 win to take the match in four.

"It's not the worst I have ever felt necessarily, but it's the worst I have ever felt after an hour and a half of a tennis match," added Murray.

"That's what was worrying about it, is it came after such a short time."

He added: "Maybe I'll speak to a nutritionist and look at what I had eaten the last three, four days."

Nick Kyrgios flirted with disqualification after being warned three times for swearing
©Getty Images



Elsewhere in the men's draw on the first day of action, top seed Novak Djokovic of Serbia eased past Argentina's Diego Schwartzman 6-1, 6-2, 6-4.

Australian teenager Nick Kyrgios of Australia came close to being disqualified during his first round match, after receiving three warnings for swearing.

But the 19-year-old, who beat Rafael Nadal at Wimbledon, overcame 21st seed Mikhail Youzhny of Russia 7-5, 7-6(4), 2-6, 7-6(1).

Meanwhile, Australian Open champion Stanislas Wawrinka won in straight sets, though was pushed to two tiebreaks against Czech Jiri Vesely before winning 6-2, 7-6(6), 7-6(3).

French Open finalist Simona Halep survived a scare to win her first round match at Flushing Meadows ©AFP/Getty Images



In the women's draw, there was an early scare for Simona Halep.

The Romanian, who was a beaten finalists at June's French Open, lost the first set against Danielle Collins of the United States in a tiebreak, 7-2.

But the number two seed regrouped to win the next two sets 6-1, 6-2 to advance into the second round.

There was a minor blip for Russian Maria Sharapova, the 2006 champion, after falling 4-2 behind in the opening set of her match against countrywoman Maria Kirilenko.

But Sharpova won the next 10 games to secure a 6-4, 6-0 victory.

Elsewhere, two-time US Open champion Venus Williams came from a set down to beat Kimiko Date-Krumm of Japan 2-6, 6-3, 6-3.

Action will resume tomorrow with women's top seed Serena Williams of the United States beginning her quest for a sixth US Open title, while Swiss Roger Federer will also begin his efforts to win the Grand Slam for a sixth time.