By Rosalba O'Brien

LONDON (Reuters) - The sound of thwacks resonated around the Olympic diving pool on Monday, with the powerful Chinese showing that even they are not infallible.

An evening of dramatic flops and mighty splashes during the men's three-meter springboard heats was capped by the unexpected sight of world champion and runaway gold medal favorite Qin Kai stepping off the board wrong, over rotating and entering the water on the diagonal.

Qin, who won the synchro gold medal five days ago, scored just 39.90 for the dive, less than half he would normally expect, but did enough on his other dives to ensure he qualified in 11th position.

"At least I got into the semi-final," he said to reporters, seemingly unconcerned. "I will improve later."

Qin was not the only one to struggle.

Russia's Evgeny Kuznetsov, silver medalist in the synchro, seemed to have sunk his hopes after he made a whale-like splash on his third dive, but also managed to just get through in 16th place, with 18 of the 30 divers qualifying for the semi-finals.

Venezuela's Edickson Contreras, however, did not have the same luck and he was left in tears after he took off wrong on the fourth dive and then made a mess of a nervy final dive, retaking the run-up and flopping into the pool.

Germany's Stephan Feck also had bad luck and had to withdraw after he failed his second dive, appearing to hurt his leg and hit the water flat on his back.

Then, to gasps from the home crowd, Britain's Jack Laugher had a 'knee buckle' on his final dive and his legs gave way, leaving him crashing to the pool with a puzzled look on his face.

The divers and coaches said it was just one of those nights, with no specific cause behind the high number of fluffed dives.

"This is the Olympic Games, everyone wanted to do their absolute best today," said British coach Adrian Hinchcliffe.

"When people go out to give everything they've got, you will see mistakes in a sport like diving. It's like golf, a slight edge and you're out in the trees."

China are aiming to sweep all eight diving titles on offer in London, and have taken the first five with consummate ease, leaving the other nations to battle it out for silvers and bronzes.

In Beijing they won seven golds out of eight, after Australia's Matthew Mitcham beat China's Zhou Luxin into silver in the men's 10 meter platform.

Qin's bad dive on Monday was a reminder that their party could yet be spoiled in London.

"We've seen the Chinese make mistakes. There's no-one safe out there in this sport," said Hinchcliffe.

Russia's Ilya Zakharov, the other silver medalist from the synchro contest, qualified in the top spot for Tuesday's semi-final.

(Editing by Greg Stutchbury)