Russia led from start to finish to take the women's event in three minutes 20.95 seconds.
World and Olympic 400 champion Wariner took the baton from Darold Williamson and sprinted away from Bahamas to give the U.S gold in 2:56.91 -- the fastest time in the world this year.
In the final event of the 10th world championships in Helsinki, Bahamas took silver with a national record of 2:57.32. Jamaica won bronze in 2:58.07.
The U.S men have won the 400 relay at every world championship since 1993, although they were retrospectively disqualified from the 2003 worlds in Paris and lost their gold medals after Calvin Harrison's suspension for doping.
Individual silver medallist Andrew Rock led the Americans off in Helsinki and handed on to Derrick Brew, the only member remaining from the 2003 finalists.
"I feel really great about how we won today. Each leg set us up to get in position," Wariner told reporters.
"Darold (Williamson) has had a long season and I felt that third leg for him was probably going to be the best position for him, just so he could relax a little more and get comfortable and put all the pressure on my back," Wariner said of his friend with a laugh.
Yuliya Pechonkina, the 400
Jamaica, Poland and Britain battled it out for the minor medals. The Jamaicans, who only qualified as fastest losers, pulled clear with 200 to go to win silver in 3:23.29. Britain edged Poland out to clinch bronze in 3:24.44.
Russia, who set the year's quickest time in Saturday's heats, were shadowed by Jamaica for half the race but Natalya Antyukh pulled clear on the third leg, giving Svetlana Pospelova an easy run to the line.
"The race wasn't easy. We thought Jamaica would be hard to beat. We wanted to run as strong as we did in the first round," said Olesya Krasnomovets, who ran the second leg.
Russia finished second in Paris two years ago behind the U.S., who were disqualified in Saturday's heats for multiple lane infractions.