Frustrated Fish ready to dig deep against Federer

Mardy Fish of the U.S. reacts during his singles tennis match against Jo-Wilfried Tsonga of France at the ATP World Tour Finals at the O2 Arena in London November 22, 2011.

LONDON (Reuters) - Mardy Fish has grafted all year to qualify for the ATP World Tour Finals and despite two defeats and his muscles screaming for mercy the American is determined to match Roger Federer shot for shot in his final group match on Thursday.

Fish, 29, was beaten 7-6 6-1 by Jo-Wilfried Tsonga in his second Group B match on Tuesday after pushing Rafa Nadal to a deciding set tiebreak on Sunday when he made his debut at the prestigious year-ender for the world's top eight.

He could hardly walk after the Nadal defeat and was clearly struggling a little physically in the second set against Tsonga when he lost the last six games in a hurry.

However, despite his slim chances of reaching the semi-finals, the world number eight and American number one said he would not be just there for the ride when he takes on 16-times grand slam champion Federer.

"That's hard to do. That's really hard to do, to be honest," Fish, who has enjoyed the greatest year of his steady but unspectacular career, told reporters.

"To just say, just enjoy the experience, go out there, and you've got nothing to lose, and go for it all. It's really not how it works.

"You have a respect level for yourself. I feel like I can win. I felt like I could win both the matches I already played, and I didn't. So we'll see how I turn up tomorrow."

Fish normally spends this week enjoying the holidays with his family and friends but any thoughts of Thanksgiving festivities back home will have to wait.

"You're going to have to prise me off the court to not be able to compete in an event like this," Fish, who lives in Los Angeles, said.

"I worked very hard this past year, these past two years, made a lot of sacrifices. These are the rewards, playing in an event like this."

Fish was visibly agitated on Tuesday as the fatigue of a long season and the desperate attempts to rehab from hamstring problems that forced him to retire from his last two tournaments appeared to catch up with him.

At one stage he had an animated conversation with umpire Carlos Bernardes and was warned for hurling his racket.

"He's seen good sides and bad sides of me," Fish joked. "That was probably a good side. It was a friendly exchange. I told him that I loved him."

Fish, however, could not hide his frustration at the recent injury problems that undermined his chances in London.

"It's disappointing because this is such a great event," he said. "You work so hard to get here for 10 months. I get all the way here and I couldn't do the things that I wanted to do before and prepare the way that I prepared basically for every tournament almost up until this one."

(Reporting by Martyn Herman, editing by Justin Palmer)