America's Nathan Adrian won gold in the men's 100m freestyle by 0.01 seconds ahead of Australia's world champion James Magnussen.
In a thrilling race, the 23-year-old was third at 50m but then turned on the power to pip the pre-race favourite in 47.52 seconds.
United States produced an Olympic-record time to win gold in the women's 200m freestyle relay final.
A brilliant final leg from Allison Schmitt led the Americans home, ahead of Australia, in a time of seven minutes 42.92 seconds.
Meanwhile, Bradley Wiggins claimed a British record seventh Olympic medal with a sensational gold in the men's time trial.
The Tour de France winner stopped the clock at 50 minutes 39 seconds for the 44km course.