By Brad Haynes

RIO DE JANEIRO (Reuters) - Brazilian duo Barbara Seixas and Agatha Bednarczuk dished out a first ever Olympic loss to American great Kerri Walsh Jennings amid a fevered atmosphere on Copacabana beach to reach the final of the women's beach volleyball.

The Brazilians won the semi-final 22-20 21-18 after midnight on Wednesday with key saves from Seixas and big blocks by Bednarczuk too much for April Ross and 38-year-old Walsh Jennings, who was aiming for a fourth consecutive Olympic gold medal in the event.

"It still hasn't sunk in what we've done, beating a player who has never lost at the Olympics," said Bednarczuk, who won the world championships last year with Seixas.

"Since the start of these Games we've been able to grow in each match, improving our concentration, our accuracy, and I think that made the difference."

Californian Walsh Jennings, nicknamed 'Six Feet of Sunshine', is a three-times world champion who was attempting to emulate long jumper Carl Lewis and discus thrower Al Oerter as the only American athletes to have won four consecutive Olympic golds in the same individual event.

But it was not meant to be as she struggled to control passes and took responsibility for the defeat, her first in 27 Olympic matches.

"It was very poor execution on my part, at the most fundamental part of the game," she said. "I put us in a hole from the start. We never gave up, but we never got our space."

The packed stands on Copacabana beach roared after every Brazilian point, the crowd backing the last local shot at gold after Germany eliminated Brazil's other team, Larissa Franca and Talita Antunes, in the other semi.

European champions Laura Ludwig and Kira Walkenhorst eased home 21-18 21-12 against the Brazilians 21-18 21-12 to become Germany's first women's team to medal in the event.

With the fans slow to fill the stadium for Tuesday's first match, the Germans seized on an unusually tranquil atmosphere to steal the opening set and walk away with the second before the Brazilian duo could hit their rhythm.

"It was really important winning the first set and we knew we had to have patience," said Ludwig. "I think I was the most nervous for this match because we were in the semi and in front of this crowd."

The final will take place later on Wednesday after the Americans play Franca and Antunes for bronze.

(Reporting by Brad Haynes; Editing by Jan Harvey/Patrick Johnston)