Felix, who took the 200 metres individual title and was part of the 4x100m team that smashed the 27-year-old world record on Friday, ran the second leg to help the Americans cross the line first.
There was to be no world record in the one-lap relay, though, with Sanya Richards-Ross powering across the line in three minutes, 16.87 seconds, outside the mark of 3:15.17 set by the Soviet Union at the 1988 Seoul Olympics.
"It was great running with these girls, we just did our best," said Felix.
"I was pumped up, I was running on adrenaline tonight. It's pretty cool. God has been so good to me, I could not do it without him."
Dee Dee Trotter, who was part of the team that won gold in Athens eight years ago, got the Americans off to a flying start and was the first in the field to hand over the baton.
"We thought it was going to be really tight, but I'm so proud of these girls, we're a great team," said Trotter.
"My job was to get us ahead of the others. We were going for some records tonight so my goal was to go out fast."
Felix, who ran a blistering second leg to set the U.S. on their way to gold in Beijing, extended that advantage to some 15 metres by the middle of the back straight on her lap.
Francena McCorory increased it further and with individual 400 metres champion Richards-Ross waiting for her at the end of her lap, only a botched baton handover was going to stop the Americans.
The transition was smooth, however, and when Richards-Ross entered the home straight, it looked like the American women might break records on successive evenings.
Richards-Ross, who won her fourth Olympic gold, came up just short but was well clear of the Russians, who finished second for silver in 3:20.23, and Jamaica who claimed bronze in 3:20.95.
"It's been phenomonal, it's been such a great experience," said Richards-Ross.