Nadal resting after ailment

London - Rafael Nadal was resting on Monday after toughing out an opening win at the ATP World Tour Championships as his stomach played up during the third set of his three-hour win over Mardy Fish.

"I do not feel not very well now? I really need to go back to the hotel and rest a little bit because I played for one hour suffering a lot," said the Spaniard after gutting through a 6-2, 3-6, 7-6 (7-3) group win over the American.

World No 2 Nadal faces a huge test on Tuesday when he plays a Group B match against Roger Federer and the end-of-season event after the Swiss marched past Jo-Wilfried Tsonga in his own opener at the weekend.

Nadal said his discomfort emerged at the start of the final set against an opponent who came to London with a groin injury and had not been expected to figure strongly in the proceedings.

Nadal is playing for the first time in six weeks after a poor showing in Shanghai in mid-October when he lost in the third round.

The magnificent physical specimen was reduced to a mere mortal as a result of his on-court tummy troubles. "When you don't feel well, you have to keep running, all the muscles are more tired than usual. The feeling of my body is not the best," said the winner of three clay trophies this season.

"But, I was there, that's a positive thing. I was mentally there all the time until the end. So that gives me victory in the first match, and a lot of confidence. For sure an important victory to try to be in the Saturday's semi-finals."

Nadal was trying to pinpoint what he ate during the day which would have caused him discomfort. "I just ate some pasta before the match. For the lunch, I had some pasta with salmon at the hotel. So nothing strange and nothing unusual.

"During the match, I started to feel something halfway through the second set, it got really worse in the beginning of the third."

Beaten opponent Fish said that while he was not at 100 percent with his groin problem which forced him from his last two tournaments, he thinks he can manage for the London week.

"Physically I felt pretty good," said the 29-year-old American. "I haven't practised that much, so it hasn't been an ideal preparation for an event like this.

"I would have liked to have had my fitness level, my lungs, a little bit fitter at this time of the year, especially coming in playing two events and then having a week off, being able to train and stuff.

"It wasn't ideal - but that wasn't the reason that I lost."