Michael Phelps won a record 19th Olympic medal as the United States took 4x200m freestyle relay gold.
The 27-year-old, who swam the anchor leg as the Americans won in a time of six minutes 59.70 seconds, now has 15 golds to his name.
Ryan Lochte put the US team in total control with a blistering first leg and they finished well ahead of France in second and China third.
Phelps overtakes Russian gymnast Larisa Latynina, who won 18 medals.
Phelps still has three more races at London 2012 before he retires and could establish a record that would be difficult to beat.
"It has been a pretty amazing career, but we still have a couple races to go," said the Baltimore swimmer, who won a record-breaking eight golds at the 2008 Games.
Just minutes before the relay victory, Phelps had claimed his 18th Olympic medal with a silver
behind South Africa's Chad le Clos in the 200m butterfly.
Le Clos came from behind to touch the wall in one minute 52.96 seconds, just 0.05secs ahead of Phelps.
"Obviously I would have liked to have had a better outcome in the 200m fly," said the American, who also won six golds at the Athens Games in 2004. "I was on the receiving end of getting touched off.
"Chad swam a great race. I've gotten to know him over the past year and he's a hard worker, tough competitor and a racer.
"It was obviously my last one and I would have liked to have won, but, you know, one minute 53 seconds isn't a terrible time."
Phelps did not have to wait long for his 15th gold, however.
The Americans had a lead of four seconds going into the last leg of the 4x200m freestyle relay - mainly thanks to Lochte's fast start.
They eventually finished 3.07secs ahead of France, with China a further 3.53secs back in the bronze medal position.
At the end of the race, Phelps, Lochte and the other two members of the team, Conor Dwyer and Ricky Berens, huddled together in an emotional moment.
"I thanked those guys for helping me get to this moment," Phelps said.
"I told those guys I wanted a big lead. And they gave it to me. I just wanted to hold on."
Great Britain's team of Robbie Renwick, Ieuan Lloyd, Rob Bale and Ross Davenport finished sixth.
Final results by Country
View full results for Men's 4 x 200m Freestyle Relay
Lochte, Dwyer, Berens, Phelps, Houchin, Mclean, Tarwater
Leveaux, Mallet, Lefert, Agnel, Stravius
Hao, Li, Jiang, Sun, Lu, Dai