By Jane Barrett

BEIJING (Reuters) - U.S. defending champions Misty May-Treanor and Kerri Walsh beat China's Tian Jia and Wang Jie to win the women's Olympic beach volleyball gold medal on Thursday.

The triple world champions screamed, leapt into each other's arms and fell into the sand after Walsh powered down the last spike to become the first team to win two Olympic beach volleyball titles.

"I'm speechless," said May-Treanor after the match.

"This has been Kerri's and my goal since the last ball dropped in Athens. It's been a lot of hard work, a lot of love, a wonderful ride," the 31-year-old added, drenched after playing in a torrential downpour.

May-Treanor and Walsh have not lost a match in more than a year and have never dropped a set at the Olympics, beating Tian and Wang 21-18 21-18 for their second gold.

"We've never defeated a U.S. team in a big final. They're just too strong for us," said Tian. "Hopefully in the next couple of years we can manage to beat them."

They may not get a chance as both May-Treanor and Walsh plan to stop competing to have children after the Games and are not sure they will come back on tour together.

It was still a good day for China, who took their first ever Olympic medals in beach volleyball -- silver for Tian and Wang and bronze earlier for Zhang Xi and Xue Chen.

The Chinese crowd yelled and screamed throughout the match, trying to do Mexican waves with their umbrellas, cheering on both home teams and even trying some beach volleyball on court between the matches.

"It is a great time for Chinese sport. I am honored to have been part of this," said Xue.

(Editing by Miles Evans)