Allison Schmitt anchored the American girls to Olympic gold in the 4x200 metres freestyle relay here.
Schmitt charged down Australia's Alicia Coutts to take gold for the US in 7 minutes, 43.92 seconds, an Olympic record.
"I knew it was going to be close," Schmitt said Wednesday.
"I was just trying to swim my own race and save legs on that first 50m, just like I did last night and bring it home strong for the US."
Coutts, meanwhile, focused on the positives.
"I got a phone call at quarter past twelve today telling me I was in the relay. I was a bit nervous coming in. Hopefully, I made the girls proud with what I did."
The Australians, who won the 4x100m relay Saturday, clocked 7:44.41, while France, the early leader, hung on for bronze in 7:47.49.