Murray crashes out

Second seed and world number four Murray seemed a touch sluggish and was broken once in the first set and twice in the second, barely registering against the unseeded Croatian's mighty serve.

At one point in the second set Murray did go 30-0 up against serve, but Ljubicic responded with four consecutive aces to epitomise the comfortable win.

Ljubicic faces David Ferrer in the semis after the Spaniard beat Robin Soderling 6-2 6-4.

World number two Novak Djokovic believes air quality is so bad in Beijing that players should be given oxygen tanks on court to help them breathe through the smog.

"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," said the top seed 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, especially if you're playing against somebody that you expect to play long rallies with.

"We had so many long rallies and it's hard to recover when you don't have fresh air," added the defending champion.

The gloomy conditions have seen the floodlights turned on early to help players and spectators see through the haze on the showcase courts at the Olympic tennis centre.

"I played in these conditions during the 2008 Olympics. There was a lot of pollution in the air, so it was not the easiest thing. But you have to accept it," added the 2008 Olympic bronze medallist.

"What can you do? I don't know. Maybe get into a chamber filled with smoke before the match, to get used to it," joked the 23-year-old.

The ATP said they would look into the air quality concerns.

A spokeswoman for the women's competition running alongside the October 2-10 event said: "WTA players have not indicated to date any adverse conditions that have had an impact on play."

The China Open in the Chinese capital is being staged 60 miles from the international climate talks in the Chinese coastal city of Tianjin.

Chinese government air monitoring differs from international standards.

Official monitoring stations describe the air as 'slightly polluted' but a device at the US Embassy in Beijing describes the air quality as "hazardous".

Fourth seed Nikolay Davydenko also crashed out of the tournament, losing 7-6(2) 6-4 to American John Isner. Unseeded Isner will next face Djokovic.