May Treanor and Walsh Jennings beat U.S. team April Ross and Jennifer Kessy in straight sets, 21-16, 21-16. The pair have never lost a match at the Olympics.
It was the Olympic farewell for May-Treanor, who has said she would like to move on.
In track and field, Southern California native Allyson Felix won the gold medal in the women's 200 meters.
Felix, from Santa Clarita, won the race in 21.88 seconds, topping Jamaica's Shelly-Ann Fraser-Pryce, who won the 100 four nights earlier, by .21 seconds. American Carmelita Jeter added bronze to go with her silver in the 100 meters.
The Americans celebrated three straight wins in track and field events. Felix's win was quickly followed by Aries Merritt's victory in the 110 hurdles and Brittney Reese's long jump title.
Claressa Shields, the newest American boxing sensation, easily defeated Kazakhstan's Marina Volnova in the semifinals of the first Olympic women's boxing tournament on Wednesday.
The 17-year-old middleweight from Flint, Mich., has earned a spot in the title bout against Russia's Nadezda Torlopova and is favored for gold.
"I'm still kind of shocked," Shields said. "I'm thinking in my head, 'Is it really true? Am I fighting for a gold medal tomorrow?"'
Shields is the last American boxer left in London after flyweight Marlen Esparza lost 10-8 to Chinese world champion Ren Cancan an hour earlier. Esparza will get a bronze medal, but Shields is the 12-member American team's only shot at gold. All nine men were eliminated in stunning fashion, leaving the winningest team in Olympic history without a medal for the first time.
The ebullient teenager won her second bout in three days against the slower Volnova with punishing right hands and relentless aggression. She forced Volnova to take a standing-eight count in each of the last two rounds after she was stunned by vicious combinations.
After her win, Shields pounded her taped right fist against her own left shoulder and screamed with joy. She laughed, raising both arms sky high as she walked to the tunnel.
The London crowd loved Shields' combination of charisma, skill and strength.
The high school junior has overcome an extremely difficult childhood. She has admitted to being sexually abused as a child by a family acquaintance. Her father, who was also a boxer, was in prison until she was 9. Her mother's boyfriend recently went to jail for shooting himself in the foot with a shotgun.
In men's volleyball, the defending Olympic champion U.S. team was eliminated from the London Games, with a straight-set quarterfinal loss to Italy.
The fifth-ranked United States struggled to defend against captain Cristian Savani, who had 19 points in the 28-26, 25-20, 25-20 victory for the sixth-ranked Italians.
The United States won the gold medal in Beijing in 2008, upsetting favorite Brazil 3-1. It was the Americans' third gold in men's volleyball, which became an Olympic sport in 1964. Russia is the only other nation with three.
Italy has never won the gold, but has won silver twice, most recently at the 2004 Athens Games.
The Associated Press contributed to this report.