LONDON: Rafael Nadal will have to wait another year to win the ATP Finals.

The world No. 1 withdrew from the elite, season-ending tournament after losing his opening match to David Goffin 7-6 (5), 6-7 (4), 6-4 on Monday at the O2 Arena.

Nadal pulled out of the Paris Masters at the quarterfinal stage 10 days ago and admitted ahead of the ATP Finals on the indoor hard-court he struggles on, that his knees, which have caused him trouble throughout his career, were still "not perfect."

Despite having qualified 13 consecutive times for the ATP Finals, only eight of which he's been fit enough to compete in, Nadal has never won the event. Spain will still be represented, as Nadal will be replaced by US Open semifinalist Pablo Carreno Busta.

"My season is finished," Nadal said. "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. I tried, but seriously was miracle to be very close in the score during the match."

After two breaks of serve each, Goffin claimed an ugly opening set via a tiebreak and was on the verge of victory in the second, but Nadal's fighting spirit saved four match points to force another tiebreaker and draw level.

However, the third set proved a step too far for the 16-time Grand Slam champion, who began to struggle with his movement and was in visible pain. Goffin secured a double break to be 4-1, but Nadal rallied once more. He could retrieve only one of the breaks.

"It was tough even if he was not moving 100 percent," Goffin said. "He was hitting the ball really hard. It's never easy to finish a match, to finish a set against him. Even if I lost four match points in the second, I had no regret. I kept going in the third."

Nadal ominously waved goodbye as he left the court, bringing to an end another auspicious season. He won his 10th French Open in June, added a third US Open in September and, at 31, became the oldest man to end the year atop of the rankings.

With the Australian Open still over two months away, Nadal was confident playing in London wouldn't have done any lasting damage.

"The good thing is (this injury is) nothing new," Nadal said. "Everybody of my team, we have the right experience on this thing. We hope to manage it well, to have the right rest, the right work, and try to be ready for the beginning of the next season."

Nadal's exit simplifies Federer's path to a seventh ATP Finals title. The winner of 2017's other two Grand Slams returns to action against Alexander Zverev on Tuesday after defeating Jack Sock on Sunday.

Making his debut at the ATP Finals earlier, Grigor Dimitrov withstood a comeback attempt from Dominic Thiem and held on for a 6-3, 5-7, 7-5 victory.

The sixth-ranked Dimitrov maintained his focus despite being narrowly denied a chance to serve out the match in the second set, and then being broken at his first chance in the third.

"Every year you learn more about yourself, about the game, about the players," Dimitrov said. "I've done also a lot of work on and off the court. It's finally starting to kind of, like, come together."