"This has been an amazing ride," said Phelps, whose record of 15 Olympic gold medals includes eight from his spectacular Beijing Games campaign.

He won six golds in Athens in 2004 along with two bronzes, and has won one gold and two silver medals so far in London.

South Africa's Chad le Clos denied Phelps his bid for a 200m butterfly triple by a hair, but silver allowed the US superstar the consolation of matching Soviet gymnast Larisa Latynina's record of 18 Olympic medals.

Phelps returned an hour later and teamed with Ryan Lochte, Conor Dwyer and Ricky Berens to capture relay gold ahead of France and China.

"I think the biggest thing I have always said is anything is possible," Phelps said of breaking Latynina's mark. "I put my mind on doing something no-one has ever done before and nothing was going to stand in my way."

Turning to his relay colleagues, Phelps said: "I told those guys I wanted a big lead in the last leg and they gave it to me. I just wanted to hold on.

"I just wanted to thank them for allowing me to have this moment.

"Before I got on the podium, I said 'sorry boys, I am not going to sing with you tonight'.There were too many emotions. I won't get a word out."

Lochte, Dwyer and Berens gave anchor swimmer Phelps a big lead, and he made it stand up against French revelation Yannick Agnel.

It was Agnel who ran down Lochte on the final lap to give France a 4x100m free relay victory.

"First gold medal of the meet, so I'm very happy," added Phelps, who had looked almost sheepish when he ascended the second step of the podium for his butterfly silver.

For most of the butterfly, it looked like Phelps would make his record-equaling 18th career medal yet another gold.

But Le Clos, third at the final turn, plunged past Phelps at the finish to win in 1 min 52.96 sec.

Phelps, who had led at every turn in a quest to become the first man to win the same Olympic swimming event at three successive Games, was just five-hundredths of a second back in 1:53.01 and Japan's Takeshi Matsuda third in 1:53.21.

Le Clos, 20, was stunned to beat a swimmer he has considered a hero ever since he watched the Athens Games.

"The legacy he has left behind for swimming is fantastic," Le Clos said. "He has changed the way they look at the sport. Everyone knows Michael Phelps."

Phelps has dominated the 200m fly for a decade. He owns the four fastest times in history and his world record of 1 min 51.51 sec is more than one second faster than the second-best performer in history.

"Just to be next to him the final was an honor itself," Le Clos added.

"I wanted to try and beat him, but when it happened in the final 25m, I couldn't believe it."

When Phelps saw the result, he flipped his cap away in disappointment.

But he was gracious in congratulating Le Clos.

"He's a hard worker and he's a very talented kid," Phelps said.

Phelps will have two more chances at an Olympic triple in the 100m butterfly and in the 200m individual medley.