World number one Caroline Wozniacki began life at the top with an injury scare on Friday, while Ivan Ljubicic completed a cull of seeds when he beat Andy Murray on yet another smoggy day at the China Open.
Second seed Murray joined Robin Soderling (third) and Nikolay Davydenko (fourth) on the scrapheap after being thumped 6-3, 6-2 by Croatia's Ljubicic in the quarter-finals.
Ecstasy turned to agony for Wozniacki less than 24 hours after she was crowned world number one when she crumpled to the ground clutching her left knee in tears while leading Serbia's Ana Ivanovic 7-6, 3-1.
The 20-year-old overstretched as she smashed a backhanded return but after taking an injury time out to get her knee strapped, she showed her champion's instinct to reach the semi-finals by shunting aside Ivanovic 7-6, 6-4.
"I felt pain when I jumped down on my knee. Not very nice thoughts went through my mind," Wozniacki told reporters.
"It was a bit of a scare. But I have had treatment and it feels better.
"It was a great feeling this morning to wake up and knowing I was the world number one but on the court it didn't feel different."
OXYGEN BOX
Air quality was so bad at the Olympic tennis centre for the third day running that top seed and champion Novak Djokovic offered a solution to the problem.
"A box of oxygen or something on the bench would be great, but we don't have it. I guess I will have to get used to it," he said after securing a semi-final place with a 6-3, 6-2 win over Frenchman Gilles Simon.
"The bad air obviously does irritate you a little bit. We had so many long rallies and it's hard to recover when you don't have fresh air," added the Serb, who is the only one among the top four seeds to reach the last four.
However, an ATP spokeswoman said: "We have not received any complaints from our players about playing conditions here in Beijing."
The gloomy conditions have seen the floodlights turned on early to help players and spectators see through the haze on the showcase courts.
But that did not help the cause of Murray, Soderling and Davydenko.
A hapless Murray failed to muster a single break point.
"I made a lot of mistakes and it was hard to get into my rhythm. He served very well. I made quite a lot of mistakes, so a combination of the two probably didn't help that much," said the world number four.
Soderling was beaten 6-2, 6-4 by Spain's David Ferrer and Davydenko handed a 7-6, 6-4 defeat by lofty American John Isner.
Unseeded Isner now faces Djokovic.
French Open winner Francesca Schiavone offered no excuses after she narrowly avoided the humiliation of a whitewash when she was thrashed 6-0, 6-2 by second seed Vera Zvonareva.
"Vera played well and it was tough for me. I'm struggling a bit with injury but that was not the reason why I lost," said the Italian.
China's Li Na, seeded ninth, used the sparse but expectant home crowd to silence Latvian Anastasija Sevastova 7-6, 6-3 and now faces the in-form Zvonareva in Saturday's semi-final.
Israel's Shahar Peer overcame Switzerland's Timea Bacsinszky 7-6, 6-4 and will battle Wozniacki for a place in the final.
