(CNN) -- Two world records tumbled in the Aquatics Centre Sunday while France claimed two golds including a stunning upset in the men's 4x100m freestyle relay.
Dana Vollmer gave the United States a winning start on the second night of swimming finals with a commanding swim in the women's 100m butterfly, becoming the first woman under the 56 seconds barrier with 55.98 seconds.
The second world record of the night saw South African Cameron van der Burgh claim the men's 100m breaststroke gold with a 58.46 seconds clocking.
The French gold rush then started with Camille Muffat in the women's 400m from American Allison Schmitt with defending champion Rebecca Adlington taking a battling bronze for Team GB.
But it was the freestyle relay which provided the most thrilling finish and a real upset as France's anchor leg swimmer Yannick Agnel overhauled Ryan Lochte to give his country its first gold in the event after a series of near misses.
The United States looked to have the gold in the bag after an improved Michael Phelps had given them a commanding lead after the second leg.
But Agnel powered past 400m individual medal winner Lochte for France to win in three minutes 9.93 seconds. Russia took the bronze ahead of fancied Australia.
The silver medal for Phelps, so disappointing in his opening final Saturday, was his 17th in the Olympics, one behind the all-time record of Larisa Latynina, a Soviet gymnast.
Earlier, Vollmer's dominance had been total as she finished nearly a second clear of China's Lu Ying with Alicia Coutts of Australia in third.
She bettered the previous world record of 56.06 seconds set by Sweden's Sarah Sjostrom, who finished fourth, at the 2009 world championships.
"I just relied on my strengths," Vollmer told gathered reporters.
"Just set it up well, passed a few people and charged it home."
Van der Burgh also broke a mark set at the 2009 championships in Rome, shaving Australian Brenton Rickard's old mark of 58.58 seconds.
He dedicated his gold to his former training partner Alexander Dale Oen of Norway, who died at an Arizona training camp in April of heart failure as the result of a blood clot.
"I just have to pay tribute to Alexander Dale Oen tonight, I know he has been with me this year, I think he helped me finish the race in such a strong manner," van der Burgh said.
"Once you have become an Olympic champion that can never be taken away from you," he added after finishing ahead of Australian Christian Sprenger and American Brendan Hansen.