NEW YORK • Mardy Fish faced down heart problems and crippling anxiety attacks, but in the end it was a humble spot of cramping which brought his career to an end.

The 33-year-old American, who has played just a handful of tournaments in the last three years and seen his ranking slip to No. 581 while battling his personal demons, had already said that this US Open, his 13th, would be his last event.

Despite serving for the match at 5-4 in the fourth set of his second-round clash against Spain's Feliciano Lopez on Wednesday, he was finally undone by the same cramping which has claimed many players at this US Open.

"I wasn't quitting. I was just cramping. I mean, both sides of both legs, if I moved anywhere close to three or four steps, two or three steps, it would go," said Fish after he lost 2-6, 6-3, 1-6, 7-5, 6-3 in 3hr 11min.

"You would have had to carry me off the court. I was definitely not stopping at that point."

Fish once reached No. 7 in the world, won six titles and made the quarter-finals three times at the Majors, including the 2008 US Open. But in 2012, his world imploded.

In May that year, he underwent a procedure to correct a heartbeat irregularity. Then, at the US Open, where he was the 23rd seed, he was set to face Roger Federer in the fourth round but stunned the tournament by withdrawing for "health reasons".

It was then that he realised he was dealing with anxiety attacks. The condition decimated his career - this year's US Open was his first since that 2012 pullout. But he hopes his legacy will be one of lifting the stigma surrounding the disorder.

"I was open and honest about a topic that is not supposed to be masculine," he said. "We are trained as tennis players from a very young age to not show weakness... I want to help people that have gone through it and try to be a role model for people that are deep into some bad times, that they can get out of it, because I was there. They can conquer it."

Lopez, a fellow 33-year-old who first played Fish back in 2002, was generous in his praise of the American.

"He was the better player and deserved to win this match. I was very lucky," said the world No. 19. "It's very sad what has happened to him with his illness in recent years. We played many times and he was often the better player."

One of the first former players to congratulate Fish on his career was compatriot and former US Open champion Andy Roddick.

"@MardyFish hell of an effort my friend... I couldn't be prouder ..... Time for that margarita," tweeted Roddick.

AGENCE FRANCE-PRESSE