Camille Muffat of France held off a strong challenge from Allison Schmitt to win the Olympic 400 metres women's freestyle gold Sunday.
Muffat, a 2011 world bronze medallist, managed to fend off the American in the final 50 metres to win in 4 minutes, 1.45 seconds, an Olympic record.
"I'm relieved and happy," Moffat said. "I haven't thought about all the work, I was thinking about the other swimmers and my family."
"Being an Olympic champion was the most difficult dream to reach. I knew this year I was the best, but I didn't expect to win."
Beijing bronze medallist Schmitt was 0.34 seconds behind, with Britain's Rebecca Adlington, 2008 gold medallist in both the 200 metres and 400 metres freestyle, claiming the bronze.
"I did not expect a medal," Adlington said. "It's a really tough race. The only disappointment is with the time."
World record holder Frederica Pellegrini of Italy was fifth.