(Adds quotes from Olympic officials)
By Crispian Balmer
BEIJING, Aug 10 (Reuters) - Rain fell on Beijing on Sunday, cooling oven-like temperatures for the second day of the Olympic Games and raising hopes that the thick haze clogging the Chinese capital might finally clear.
The rain delayed the start of the tennis competition on Sunday morning. Optimistic Olympic officials said the grey mist shrouding many venues should lift in the coming hours.
"I think the blue skies will come, especially after today's rain. I've got my fingers crossed. Hopefully tomorrow will be better," said Wang Wei, secretary-general of the Beijing Organising Committee for the Olympic Games.
A third of the riders in Saturday's men's cycling road race failed to finish and tennis officials had said they were considering heat breaks to help players cope with the stifling humidity and high temperatures.
Smog has also been a persistent problem for Beijing, with billions of dollars spent on a clean air plan that took half the city's 3.3 million cars off the road ahead of the Aug. 8-24 Games and closed dozens of factories around Beijing.
The International Olympic Committee (IOC) had warned it might reschedule events if the air quality posed a threat, but on Sunday it said there were no problems.
"The readings that we were looking at indicated that we have no cause for concern at this stage," said IOC spokeswoman Giselle Davis. The Games' organisers have a 72-hour monitoring system in place in Beijing to predict future weather patterns.
Saturday's cycling race appeared to confirm some athletes fears about the difficulties of competing in Beijing when 53 of the original 143 riders pulled out of the gruelling 245-km (152.2 miles) cycling road race past.
"It feels like you're at 3,000 metres because of the air. You cannot breathe. The air is thick and there is smog ... Right now, I'm just knackered," said German cyclist Stefan Schumacher after pulling out of the race.
Beijing's Wang insisted that conditions were safe.
"We seem to be stuck in a weather pattern that is bringing us high humidity and higher than normal temperatures ... but despite all this, the air quality continues to remain in the satisfactory range that does not pose any threat to the athletes," he said.
The official weather forecast said temperatures in central Beijing would be 26 Celsius (79F) on Sunday after hitting 35 Celsius (95F) in recent days. Showers were also expected in Hong Kong, the host to Olympic equestrian events.
Achim Steiner, who heads the U.N. Environment Programme, said many of the 30,000 journalists covering the Games were over-fixated on pollution.
Steiner said athletes were right to be worried about the smog but China deserved praise for reducing pollution over the past decade even as its economy has ballooned. (Additional reporting by Kirby Chien and Karolos Grohmann; editing by Keith Weir) ((For more Olympic stories visit our multimedia website Road to Beijing" here; and see our blog at blogs.reuters.com/china))