* Holders U.S. trounce Germany, Australia beat Britain
* Bulgaria stun Poland, Brazil outfox Russia (Recasts with later matches)
By Mark Meadows
LONDON, July 31 (Reuters) - Favourites Brazil and holders the United States won as expected on Tuesday but Bulgaria's Tsvetan Sokolov sent mini-shockwaves through the men's Olympic volleyball with a booming serve that floored fancied Poland 3-1.
At a rocking Earl's Court Arena decked out with the flags of the competing nations, the second round of six pool matches came and went in a blur of blocks and spikes with only Sokolov's prodigious leap and Pete Sampras-like serve standing out.
The U.S were perfectly efficient in their easy 3-0 win over Germany while world champions Brazil sparkled in patches in a 3-0 success over Beijing bronze medallists Russia, but the wow factor came in the early east European clash.
Poland, who should still easily make the last eight with the top four in each six-team group going through, had almost the perfect build-up to the London Games after victory in the World League this month cemented their place as gold medal hopefuls.
Bulgaria's preparations had been nothing short of farcical with their coach and best player quitting immediately after Olympic qualification in a row with federation bosses.
Yet with Poland virtually playing as a home team in front a fervent 15,000 fans in west London, which boasts a large Polish community, Bulgaria turned the tables in style to top Pool A as the only side on a maximum six points from two matches.
With three preliminary games left, much-hyped Poland know they must rediscover the form from Sunday's triumph over Italy.
"We want to write our own future, to give our fans joy and make them happy," a confident Bartosz Kurek, Poland's most talked about player, told Reuters.
Despite a cacophony of boos every time he took the ball, towering Bulgarian Sokolov jumped high into the air and boomed down a series of high-powered slapped serves that would not have looked out of place on the tennis lawns of Wimbledon.
American mainstay Clayton Stanley produced 13 winning spikes as Germany folded 25-23 25-16 25-20 in an hour and 23 minutes on the peach and turquoise court at the soon-to-be-demolished art deco venue.
Russia refused to be ripped apart and Brazil, who rested inspirational captain Giba, needed every ounce of their experience to prevail in three tight sets and join the U.S. on top of Pool B with two wins from two.
Serbia beat Tunisia 3-1 to notch up their first win in Pool B with Uros Kovacevic playing instead of his older brother Nikola, 10 years his senior and still in the squad.
"Everyone is fighting for positions in the team, he played before. You can't be a rival with your own brother," Uros told Reuters.
"Serbia can go far, we need to go into every game in the best shape possible."
Italy got their first points on the board in Pool A with a 3-1 win over Argentina, who are also on one win along with Poland and Australia, 3-0 victors over point-less Britain.