On Sunday, Serena Williams earned a second gold medal at the London Games, and this time did it with the help of her sister Venus.

The American sisters defeated Andrea Hlavackova and Lucie Hradecka of the Czech Republic 6-4, 6-4, on Centre Court. The sisters also won gold in doubles at the 2000 and 2008 Games.

Venus had also won a gold in singles in the Sydney Games in 2000.

"Crazy," Serena said. "I'm always copying her. I forgot that she did it in Sydney and I do it here. We're the same doubles team, we just split this to singles, so it's cool."

On Saturday, Serena held off Russia's Maria Sharapova to win gold. With the singles victory, she joined German Steffi Graf as only the second woman to win a career grand slam, which consists of all four grand slams and the Olympics.

It's been a dominant effort for U.S. tennis in London. The Bryan brothers, Bob and Mike, earned the gold in men's doubles on Saturday.