Last Updated 3:54 p.m. ET
(AP) LONDON - Dana Vollmer won a gold medal at the Olympics and set a world record, too.
Not bad for someone who didn't even qualify four years ago.
On a night featuring a relay duel between the Australians and the Americans, Vollmer got things started with a bang Sunday in the 100-meter butterfly. She was third at the turn but powered to the wall for a time of 55.98 seconds, beating the record of 56.06 set by Sweden's Sarah Sjostrom in a since-banned high-tech bodysuit at the 2009 world championships.
The American dropped back her head when saw the time, then broke into a huge smile, slapped the water and pumped her fists.
"I'm on top of the world right now." she said. "I still know I can go faster."
Also on Sunday, Camille Muffat of France edged Allison Schmitt of the United States by less than half a stroke to win the Olympic 400-meter freestyle.
Muffat clocked an Olympic-record 4 minutes, 1.45 seconds, while Schmitt was second in 4:01.77.
Defending champion and local favorite Rebecca Adlington made a late charge to take bronze in 4:03.01 for Britain's first swimming medal in the London Games.
Two-time world champion Federica Pellegrini of Italy finished fifth.
Vollmer, who made the Olympics as a 16-year-old in 2004, was a huge disappointment when she failed to make the team in Beijing in 2008. She was slowed by injuries and health problems, making her question whether she even wanted to continue swimming.
But her injuries healed and a change in diet gave her a new outlook. She came close to breaking Sjostrom's record at the U.S. Olympic trials last month, and set an Olympic record in the semifinals to come in as the top qualifier.
Now she's an Olympic champion.
"I kept telling myself that my strength is my second 50," Vollmer said. "I kept really calm."
Lu Ying gave China another medal at the Olympic Aquatics Centre, taking silver in 56.87. Australia's Alicia Coutts grabbed the bronze in 56.94.
"It's not bad," Lu said. "It's the result, more or less, I hoped for."
It was a tough night for Sjostrom. Not only did she lose her world record, she didn't even get a medal, touching fourth in 57.17.
Vollmer was the second swimmer to set a world record at the London Games, and only the fourth to break a mark set during the rubberized suit era. Those suits were banned after an astonishing 43 world records were set at the 2009 world championships.