Serb protest rejected

The American trailed Serbian swimmer Milorad Cavic for the whole race and was well behind with just 15m to go but he finished like a train to prevail by just 0.01 seconds.

However, video footage on who touched first proved inconclusive, with some angles even suggesting Phelps was not ahead at the wall.

Serbia lodged a written protest but after officials reviewed footage and the electronic timing systems they declared themselves satisfied with the result.

The Serbs, according to an official, were also placated having had the opportunity to access the same information available to the referee.

Phelps' victory allowed him to equal Mark Spitz's record but there was a feeling around the Water Cube that officials had been too quick to award the gold to the American.

However, race referee Ben Ekumbo defended their integrity.

"Immediately after the men's 100m butterfly we got an official, written protest from Serbia which was questioning the arrival [of Phelps] as being too fast," said the official from FINA, the sport's governing body.

"Under our rules we do listen to protests. We looked at video footage and it was very clear the Serbian swimmer touched second, after Phelps. One was stroking and one was gliding.

"Two independent timing systems showed exactly the same on the time. Phelps was 50.58, Cavic was 50.59. The automatic timing systems are in perfect order and there are no doubts."