Russian runner Natalya Antyukh has held off a late surge from Lashinda Demus, the current world champion from the United States, to win Olympic gold in the women's 400-meter low hurdles.
Antyukh ran a personal best of 52.70 seconds to win her second Olympic medal. She won bronze in the 400 meters at Athens in 2004.
Demus took silver by finishing in 52.77 seconds, and Zuzana Hejnova claimed bronze for the Czech Republic with a time of 53.38 seconds.
In other track and field events on August 8, Brittney Reese of the United States won the Olympic gold medal in the women's long jump with an effort of 7.12 meters.
Russia's Yelena Sokolova won the silver with a 7.07-meter jump, while Janay DeLoach of the United States won the bronze.
Meanwhile, the Russian men's basketball team reached the final four of the London Olympics tournament with an 83-74 victory against Lithuania.
Russia will face Spain on Friday after the Spanish team defeated France 66-55. A victory against Spain would ensure Russia wins a medal in London.
It would also mark the first time since the breakup of the Soviet Union that Russia wins an Olympic medal in men's basketball.
Russia defeated Spain 77-74 during an earlier tournament game in the London Olympics.
In other games, Argentina defeated Brazil 82-77 to advance to a semifinal match-up against the United States, which defeated Australia 119-86.
In men's water polo, three former Yugoslav countries -- Serbia, Montenegro and Croatia -- advanced to the final four on August 8. Montenegro will play Croatia on August 10 while Serbia faces Italy.
Serbia's bench celebrates a goal against Australia during their quarterfinal water-polo match.
Montenegro beat Spain 11-9 in their quarterfinal to give their country a chance to win its first Olympic medal as an independent nation.
Croatia made the final four with an 8-2 victory against the United States on August, and Italy advanced with an 11-9 victory against Hungary, which has won the gold in the last three Olympics.
Gold-medal favorites Serbia were nearly upset by lower-ranked Australia but staged a decisive comeback in the second half to win 11-8.
Also on August 8, Sarah Attar became the first female track-and-field athlete to represent Saudi Arabia at an Olympics when she competed in the 800-meter preliminary heats.
The 19-year-old -- who wore a white head cover, a long-sleeved green top, and black leggings -- received a generous ovation from a capacity crowd at the Olympic stadium as she trailed in last out of the eight runners in her heat.
Attar has dual U.S.-Saudi citizenship and is a student at Pepperdine University in Los Angeles. She is the second Saudi woman to compete in any Olympics, following judoka Wojdan Ali Seraj Abdulrahim Shaherkani's earlier competition in London.
The International Olympic Committee (IOC) had extended a special invitation to Shaherkani and Attar after it pressed Saudi Arabia to end its ban on participation by women.
Away from the competition, the IOC confirmed that seven athletes from Cameroon are missing.
The IOC said it was officially notified in writing by Cameroon's Olympic Committee about their disappearance.
David Ojong, the head of the Cameroon delegation, said five boxers, a swimmer, and a female soccer player have been missing since the weekend. The reason for their disappearance is not known.
Ojong said the athletes had visas allowing them to stay in Britain until November.
London Olympic officials said Cameroon's Olympic delegation is seeking help finding the athletes.
With reporting by Reuters, AP, AFP, dpa, and BBC