By Estelle Shirbon

LONDON (Reuters) - A pair of Russian newcomers upset Beijing bronze medalists Zhang Xi and Xue Chen of China in a close Olympic women's beach volleyball opener on Saturday that set pulses racing.

The surprise result spiced up the first day of competition, in which the top attraction will be a clash between double gold medalists Misty May-Treanor and Kerri Walsh of the United States and Australians Natalie Cook and Tamsin Hinchley.

Low-ranked Anastasia Vasina and Anna Vozakova beat the Chinese pair, who are among the favourites to win gold in London, in three sets.

"We won't look back on this match. I wear a lucky jade necklace but it wasn't lucky for me today," said Zhang.

The Chinese still have a chance for a medal as the tournament starts with a pool stage before progressing to a knock-out phase.

"The atmosphere was perfect and we are really enjoying London. We just need to focus," said Xue.

Beach volleyball is scored using a best-of-three-sets system. The first two sets are played to 21 points and if each team wins one, a third set is played to 15 points. All sets require a two-point advantage to win.

Vasina and Vozakova beat Zhang and Xue 2-1 (18-21, 21-14, 16-14).

The Olympic beach volleyball event is being staged at Horse Guards Parade, a vast esplanade in the heart of London's government district of Whitehall. The venue is right next to Number 10 Downing Street, official residence of British prime ministers, and a stone's throw from Buckingham Palace.

From the 15,000-seat stadium, the biggest in Olympic beach volleyball history, spectators enjoy a stunning view including the London Eye Ferris wheel gently spinning by the Thames river.

The showdown between May-Treanor and Walsh, who won gold in Athens in 2004 and Beijing in 2008, and Cook and Hinchley, is scheduled for 11:00 p.m. (2200 GMT).

Cook, the first Australian woman athlete to compete in five Olympic Games, won bronze in Atlanta in 1996 and gold in Sydney in 2000 with her then team mate, Kerri Pottharst.

May-Treanor and Walsh are favourites to win the match although Cook and Hinchley have been on impressive form.

"She (Cook) has always been a true competitor. She's fun to play against. She's very feisty. We're looking forward to facing her on the first night," May-Treanor said before the Games.

Cook sounded a little less bullish.

"The first game out is not where we would have liked to have seen them," she said at pre-Games press conference. "We hope to catch them sleeping."

(Editing by Matt Falloon)