Reigning China Open champions Novak Djokovic and Serena Williams experienced contrasting fortunes at the tournament Friday, with the men's top seed powering through to the semi-finals, while Williams withdrew injured.
Djokovic, who has an incredible 100 percent record at the $5.4 million tournament, beat fifth seed Grigor Dimitrov 6-2, 6-4.
The world number one was again highly emotional on the Diamond Court at China's National Tennis Centre, smashing his racket twice in the second set in frustration.
The Serb broke his Bulgarian opponent's service twice in the first set, after saving three break points in the third game.
He appeared to be heading for a routine victory at 5-3 and serving for the match in the second set, but Dimitrov broke serve to temporarily halt Djokovic's advance.
But Djokovic took the next game and wrapped up his victory in 90 minutes.
He described his refusal to hand Dimitrov his serve early on as a "big" moment, and was pleased with his performance.
"That was pretty big. I mean, we both started a bit rusty on the court, lot of unforced errors. So it took a little bit of time to get into the groove, to get into the rhythm," Djokovic said.
"Pretty slow conditions because of the weather. It's a bit cold today, which I think suited more to my style of the game. And I was trying to mix up the pace, give him high balls to the backhand, serve efficiently.
"Everything worked well. The second set was up and down. But generally was a good performance."
Djokovic 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 in Beijing won his quarter-final against Croatian Marin Cilic 6-1, 6-4.
Murray crushed his opponent in the first set, breaking serve three times. He was then forced to wait until the final game of the second set to break again and clinch victory.
The 27-year-old Scot is bidding for a 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, Rafael Nadal and Roger Federer -- 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.
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.
- Serena 'frustrated' -
In the women's competition, world number one Serena Williams withdrew from the tournament with a left knee injury.
The reigning champion in Beijing 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 has enjoyed a return to consistency in China after a poor run in the North American swing.
The Czech player 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 Ivanovich for a place in the final.
Ivanovich 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 October 5.