Beijing - Rafael Nadal has crashed out of the China Open Friday, tiring at the end of a gruelling three-set quarter-final against qualifier Martin Klizan, while reigning women's champion Serena Williams withdrew injured.
In only his third outing since returning from three months on the sidelines, 14-times Grand Slam winner Nadal managed just two points in the last four games of a match that he lost 6-7 (7/9) 6-4, 6-3.
The world number three won the first set at the tie break, and was 4-3 ahead in the second before Slovakia's Klizan fought back and forced a decider.
The second seed then appeared to be edging through to the semi-finals after breaking serve in the third set to make it 3-2 in his favour.
But Klizan, who is ranked 56th by the ATP, then tore into Nadal, taking nine consecutive points in quick succession and the final four games as he closed in on victory.
Before Beijing, Nadal had not played competitively since he was dumped out at Wimbledon by 19-year-old Australian Nick Kyrgios.
He was then struck down in training by a right wrist injury which forced him to miss the US Open.
The nine-time French Open champion looked more composed during the previous two rounds in the Chinese capital, which he won in straight sets.
But the quarter-final loss was a grim awakening that it may be a while until he is back to his world-beating best.
"It will not be easy after what happened," Nadal said.
"Always when you are outside for a few months, as I said the other day, is not the same as if you are coming back the next season that everybody starts from zero.
"You are coming back now, and the other players are on the road, are in rhythm. Physically you feel more tired."
Klizan will meet third seed Tomas Berdych in the semi-finals, after the world number six Czech beat American John Isner, his doubles partner, 6-1, 6-4.
Reigning champion Novak Djokovic powered through to the last four as he overcame fifth seed Grigor Dimitrov 6-2, 6-4.
"Everything worked well. The second set was up and down. But generally was a good performance," the world number one said.
The Serb is bidding for his fifth title in Beijing, a tournament he has won every year since 2009 -- apart from 2011, when he did not take part.
He will now face Briton Andy Murray in the semi-finals after the sixth seed won his quarter-final against Croatia's US Open champion Marin Cilic 6-1, 6-4.
Murray broke serve three times in the first set but was forced to wait until the final game of the second set to break again and clinch victory.
The 27-year-old Scot is vying for his second consecutive title in China after he won in Shenzhen last weekend.
He is desperately chasing points as he pushes to qualify for the ATP World Tour Finals next month, which features the top eight men's players.
Only five berths are available as the world's top three players -- Djokovic, Roger Federer and Nadal -- have already confirmed their place for the London tournament.
Murray is in ninth position and is aiming to pick up points in Beijing and at the Shanghai Masters next week. Berdych meanwhile, holds the eighth berth.
The duel between Murray and Djokovic Saturday will be a re-match of their epic US Open quarter-final, which Djokovic won 7-6 (7/1), 6-7 (1/7), 6-2, 6-4.
In the women's competition, world number one Serena Williams withdrew from the tournament with a left knee injury.
The reigning champion was due to play Australian Samantha Stosur after winning her third round match Thursday evening with a bandaged knee.
"It's really frustrating, especially from here. This is a really big tournament for me. I'm defending champ," the 33-year-old said.
Stosur, the 2011 US Open winner and former world number four, will now go straight into the semi-finals where she will play Petra Kvitova.
Third seed Kvitova beat Italian Roberta Vinci 7-6 (7/2), 6-4 to book her place in the last four.
The world number three won the inaugural Wuhan Open last Saturday, her third title of the year.
Fourth seed Russian Maria Sharapova won her quarter-final match against compatriot Svetlana Kuznetsova 6-0, 6-4.
The victory means she will face ninth seed Serb Ana Ivanovic for a place in the final.
Ivanovic made the last four following the withdrawal of her scheduled quarter-final opponent Simona Halep on Thursday. The Romanian world number two retired after her three-set victory against Andrea Petkovic in the third round.
The $5.4 million China Open will reach its climax on Sunday.
Results from the China Open on Friday (x denotes seeding):
Novak Djokovic (SRB x1) bt Grigor Dimitrov (BUL x5) 6-2, 6-4
Andy Murray (GBR x6) bt Marin Cilic (CRO x4) 6-1, 6-4
Tomas Berdych (CZE x3) bt John Isner (USA x8) 6-1, 6-4
Martin Klizan (SVK) bt Rafael Nadal (ESP x2) 6-7 (7/9) 6-4, 6-3
Petra Kvitova (CZE x3) bt Roberta Vinci (ITA) 7-6 (7/2), 6-4
Samantha Stosur (USA) bt Serena Williams (USA x1) - walkover
Maria Sharapova (RUS x4) bt Svetlana Kuznetsova (RUS) 6-0, 6-4
Ana Ivanovic (SRB) bt Simona Halep (ROM) - walkover