Michael Phelps swam into history Tuesday, becoming the most successful Olympian of all time as a 4x200m freestyle relay gold gave him a record 19th medal after silver in the 200m butterfly.
"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 treble 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-equalling 18th career medal yet another gold.
But Le Clos, third at the final turn, plunged past Phelps at the finish to win in 1min 52.96sec.
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 night belonged to Phelps, who swam the anchor leg of a relay that the Americans dominated from start to finish after Ryan Lochte handed them a commanding lead.
It was a historic moment in the 116-year annals of the modern Olympic Games, and an emotional one for Phelps, still a powerful force but no longer the commanding figure who won an unprecedented eight golds at the Beijing Games in 2008.
"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 1min 51.51sec is more than one second faster than the second-best performer in history.
Is Phelps the greatest?
The debate on the greatest Olympic athlete was reopened when Michael Phelps anchored the US men's quartet to a sweeping victory in the 4x200 metres freestyle relay at the London Games.
Consequently, Phelps overhauled Soviet gymnast Larisa Latynina's previous record medal tally of 18 to a standing ovation at the London Aquatic Centre.
"Is he the greatest of all time?," shouted the venue announcer as Phelps and his team mates walked around the pool displaying their gold medals.
Possibly, would be the honest if unsatisfying answer once the euphoria has dissipated.
The Michael Phelps of 2012, the light visibly fading, is not the phenomenon who won a record eight gold medals in Beijing four years ago.
So far he has failed to win an individual gold and also failed to become the first male swimmer to win three successive titles when he finished second in the 200 metres butterfly final earlier on Tuesday.
Michael Phelps' days of seemingly effortless dominance are done, but the Olympic accolades continue to pile up for the superstar even as he looks toward a life beyond swimming.
"When I'm finished in London, if I can look back on my career and say I've done everything I've wanted to do -- putting the medals, the records and this and that aside -- if I can say I'm happy, that's all that matters," Phelps said ahead of his his fourth and final Olympic campaign in London.
Phelps is the first US male swimmer to make four Olympic teams, and after three medals in London he has become the most decorated athlete in Games history, in any sport.
But for a time after his Beijing glory days it was unclear if he would even make the attempt.
A tabloid photo fracas in 2009, when a British newspaper ran a picture of him with a marijuana pipe, created an outcry that had him reconsidering his plans to continue swimming through 2012.
Even after his mind was made up, Phelps found himself paying the price for his indecision and lack of motivation in training as rivals such as US team-mate Ryan Lochte surged to the top of the sport in 2010 and 2011.
Dismayed at times by Phelps' lack of commitment, long-time coach Bob Bowman said he has come to respect the fact that Phelps has unapologetically carved his own path to London.
"The one thing that I think I'm the most proud of Michael about, which took me forever to realize, is he's accomplished all these things, he's decided to do other things, he came back to it -- but he did it absolutely his way, the way he wanted to do it," Bowman said.
"He made all those decisions, he stood by them, he never made an excuse, he's always been straight up-front about where he is, what he's done, what he wants to do, and I think that's admirable."
For Phelps, London is about putting a final gloss on a career that has seen him mature from a restless kid who found an outlet for his energy in the water, to a cross-over star with all the trappings of modern celebrity.
(with inputs from AFP, Reuters)