The U.S. foursome of DeeDee Trotter, Allyson Felix, Francena McCorory and Sanya Richards-Ross were never seriously challenged, grabbing a 10-meter lead after the first leg by Trotter and never looking back. With three clean handoffs, Richards-Ross took the baton on the final leg with a 40-meter lead and never relented, holding that margin through the anchor and capturing gold in 3:16.87. The time was the third fastest in U.S. history.
"We thought it was going to be really tight," Trotter said. "… My job was to get us ahead of the other. We were going for some records tonight so my goal was to get out fast."
"These ladies made it too easy for me," Richards-Ross said. "It was really fun to be able to go out with such a great lead and to secure it from my teammates and bring home gold. It was just phenomenal to be on my third 4x400 [Olympic] team. It just shows the kind of depth the U.S. has in this event. I'm excited about the future."
Heading into Saturday night, the U.S. women hadn't lost the 4x400 relay since the 1992 Barcelona Games, carrying a streak of four straight gold medal finishes. Felix and Richards-Ross had a hand in one of those finishes, both running in the 4x400 relay final in Beijing.
Exactly how dominant has the U.S. been in the event? Their toughest competitors – the Russians – entered the race with their game plan built around finishing second.
"We talked about winning silver," Russia's Tatyana Firova said. "We wanted gold, but USA are too strong and it wasn't possible to win. They are a very strong team."
But even the U.S. team was shocked at the final margin heading into the last 100 meters. With the Americans ahead by 40 meters, Richards-Ross adjusted her plan to a more conservative finish, making sure she didn't overextend herself and risk an injury that could jeopardize a sure win.
"For sure on paper, I thought it was going to be much closer," Richards-Ross said. "The Russians looked really strong. So did the Jamaicans and the Brits. I thought it was going to be close and I was looking forward to that. After DeeDee's leg and Allyson's leg, I thought, 'Oh my gosh.' It is a little challenging to run from [so far in] front, because you don't want to go too fast. You don't want to mess it up. So I kind of just ran a safe leg, to be sure that if anything happened, I could get home strong.
"It was very exciting to come out to these Games, when people are giving their absolute best, and to dominate like that was just impressive to me."
The win is the 12th medal overall in track and field for the American women – and sixth gold, including wins in the 200 meters, 400 meters, long jump, pole vault and a world record in the 4x100 relay. Felix, who said she was "running on adrenalin" Saturday, played a pivotal part in all of that success, with the 4x400 win giving her three golds in London (to go with her 4x100 and 200 wins). She is also only the second American woman to win golds in the 4x100 and 4x400 relays in the same Games, joining Chandra Cheeseborough who did it in Los Angeles in 1984.
The 4x400 was also the second gold for Richards-Ross. Felix now has six Olympic medals in her career (including four golds), while Richards-Ross has five (also four golds).
Related Olympics coverage on Yahoo! Sports:
More Olympics coverage on Yahoo! Sports:
• Video: Spice Girls reunion headlines Olympic Closing Ceremony
• U.S. track medalists under fire for relationship with man banned from sport
• Top 10 U.S. athletes to watch at Rio Summer Games