TENNIS: World No.1 Rafael Nadal has pulled the pin on his season after a first-up defeat in the ATP Finals to Belgian David Goffin.

Nadal (pictured) lost 7-6 6-7 6-4 in London and afterwards admitted he had lost his fitness battle and would have to withdraw from the season-ending tournament.

The Spaniard came into the tournament after pulling out of the Paris Masters with a knee injury, but after initially believing he could get through the finals, he had to admit defeat.

"No, I am off,” Nadal said. "My season is finished.

"Yeah, I had the commitment with the event, with the city, with myself.

"I tried hard. I did the thing that I had to do to try to be ready to play.

"But I am really not ready to play. Is about the pain.

"I cannot hold with enough power to keep playing.

I tried, but seriously it was a miracle to be very close in the score during the match. It really doesn't make sense.”

Nadal said he would work hard to be ready for the start of the next season.

"I know what I have to do,” he said.

"I know all the things that happened in the past when I had these things, and I know the treatment that I had to do. I know the periods of time that I need to work. Then if the treatment works or not, we will see.”

Earlier, also in the Pete Sampras group, Grigor Dimitrov beat Dominic Thiem 6-3 5-7 7-5.