LONDON (Reuters) - Twice Olympic beach volleyball champions Misty May-Treanor and Kerri Walsh will battle for a third gold in an all-American women's final against Jennifer Kessy and April Ross on Wednesday.

May-Treanor and Walsh are the only pair of either gender to successfully defend an Olympic title in beach volleyball since the sport's Games debut in Atlanta in 1996. They won gold in Athens in 2004 and again in Beijing in 2008.

Kessy and Ross, world champions in 2009, have been one of the strongest teams on the circuit for several years but they are usually in the shadow of May-Treanor and Walsh.

Wednesday's final is a rare opportunity for the number two U.S. pair to take the spotlight away from their illustrious compatriots.

Appearing in their first Olympics, Kessy and Ross were expected to do well, but it was still a shock when they beat Brazilian world champions Juliana Felisberta and Larissa Franca by two sets to one (15-21 21-19 15-12) in Tuesday's semi-final.

They are unlikely to be given an easy ride by May-Treanor and Walsh, who have said they want to crush all their opponents regardless of where they are from.

The defending champions fought off a dynamic Chinese duo in the semi-finals. Zhang Xi and Xue Chen, bronze medalists in Beijing, raced to an early lead against May-Treanor and Walsh but the Californians kept cool under pressure, deployed some imaginative tactics and won two sets to nil (22-20 22-20).

On paper, May-Treanor and Walsh are favorites to win against Kessy and Ross. Out of 13 previous matches between the two teams in international tournaments, the Olympic champions have won 11 while Kessy and Ross have won two.

But after their stunning performance against Larissa and Juliana, who were the number one seeds and initial favorites to win gold, Kessy and Ross go into the final with strong momentum.

The match is scheduled for 2000 GMT in the 15,000-seat stadium built for the Games at Horse Guards Parade, a stunning location next to Prime Minister David Cameron's residence at 10 Downing Street and within sight of Buckingham Palace.

Britain's Prince Harry, who was photographed playing beach volleyball during a recent trip to Brazil, is expected to attend.

At 1800 GMT, Juliana and Larissa will face Zhang and Xue in the bronze medal match.