By sportswriter Lou Chen

    BEIJING, Aug. 16 (Xinhua) -- American mega-Olympian Michael Phelps equaled Mark Spitz' seven-gold mark after winning the 100-meter butterfly by the smallest margin in a sport at the Beijing Olympic Games here on Saturday.

    Phelps out-touched runner-up Serbian Milorad Cavic by 0.01 second with an Olympic record time of 50.58 seconds. Australian Andrew Lauterstein got the bronze in 51.12. World record holder Ian Crocker of the United States finished fourth in 51.13.

American Michael Phelps won the men's 100m butterfly gold medal at the Beijing Olympic Games on Saturday.(Xinhua/Wang Dingchang) Photo Gallery>>>

    The gold medal, seventh in Beijing, has brought his total Olympic gold tally to 13.

    "I think it really shows that no matter what you set your imagination to, anything can happen," Phelps said. "Some people said it would be impossible to duplicate and that it wouldn't happen. It shows really that anything can happen."

    "I am in a sort of dream world. Sometimes I have to pinch myself to make sure it is real. I am happy I am in the real world," he said.

    In the two-lap event, Phelps came upon the deck as the defending Olympic champion. But his gold medal was at stake when he touched wall the seventh in the first 50 meters, about half a body length behind Cavic. Phelps splashed ahead in the second 50 meters and finally outstroked Cavic amid jittery cheers of the spectators.

    After the race, the Serbian team filed an official protest to question the scores, but race referees and swimming governing body FINA officials insisted the result is valid. "Accoridng to our rules, we used the automatic timing system, which was in perfect condition and perfect order," said head referee Ben Ekumbo.

    "We looked at video footage. It was very clear that the Serbian swimmer touched second after Michael Phleps. It's evident from the video that it was an issue of stroking. One was stroking and the other was gliding," he said.

    The Serbian team has accepted the ruling, he added.

    Phelps himself was also surprised at the table-turning result. "When I took that last stroke I thought I lost the race there, but it turns out that was the difference," he told reporters.

    "If I had have glided, I would have been way too long. I took short faster strokes to try and get my hand on the wall, and I ended up making the right decision, it turned out to be in my favour," he said.

    The winner said he had no knowledge of the protest.

    Phelps said he took the race benchmarking himself against teammate Crocker. "I race against him all the time... when I saw Crocker at the turn, I knew Cavic would be somewhere with him, I could sort of see him out the corner of my eye," he said.

    Before the race, his coach Bob told him it would be probably good for the sport if he lost. "When he said that I was fired up. I said, 'I'm going to go for it'. And when I saw that finish I said 'wow'," Phelps said.

    The champion again screamed after the victory and punched hard at the water. He was so overjoyed that it took him a while to notice Cavic congratulating him in the pool.

    "I feel a little bit of everything - relief, excitement, everything. I had to take my goggles off first to make sure the one was next to my name," he said.

    With the hard-won gold medal, the unstoppable Phelps has removed the biggest obstacle on his way to an unprecedented feat of eight golds at a single Olympics.

    Phelps' chances of the eighth gold, vested in the 4X100m medley relay, seems a sure bet as the Americans have championed the relay in the last ten Olympics.

    Already looking ahead, Phelps said his ultimate goal is to change the sport of swimming in a way. "I just got a picture from my friend from the sports center live, they aired the race. They had it live on a 'Jumbotron' in the middle of a baseball game. So my goal is starting to happen, but I have a long way to go with that," he said.

    "I am sure Bob and I can think of some more goals in the next four years," he said.