Argentina's players celebrate victory against Bulgaria after their men's Group A volleyball match at Earls Court during the London 2012 Olympic Games August 4, 2012. (Photo : REUTERS/Ivan Alvarado)
Argentina overcame Bulgaria and Russia rallied to defeat the U.S. holders in Saturday's Olympic men's volleyball as the two group frontrunners were beaten for the first time.
Brazil, who are also tipped for a medal, narrowly avoided defeat against Serbia who pushed them all the way in a Group B five-setter that lasted well beyond midnight.
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The Brazilian support roared just as loud even as the stands emptied.
Put under huge pressure by the Serbs, South American tempers flared in the fourth set at some refereeing decisions before they showed their class in the fifth to win 22-25 25-15 20-25 25-22 15-9 to book a place in the quarter-finals.
The defending champions from the U.S. went through after hanging on to first place in Group B despite losing to the Russians who also clinched a spot in the last eight.
Bulgaria were top of Group A before losing to Argentina and are still guaranteed to qualify despite their 18-25 25-21 25-19 25-20 defeat.
Poland are now first in that section after recording a three-set victory over hosts Britain.
The teams all have one match remaining in the round-robin stages, with the top four in each group progressing to Wednesday's quarter-finals.
Italy are also through after recovering from two sets down to defeat a young Australian side.
Russia saved a match point on the way to victory over the Americans.
The Russians, bronze medalists in Beijing in 2008, clung on at the end of the third set before knocking the stuffing out of the U.S. to win 27-29 19-25 26-24 25-16 15-8.
"Russia started to wake up and started to play better. They realized they had to serve more aggressively and they did and that was what changed the game," American David Lee told reporters.
"This is definitely a team that we're going to see later on in this tournament."
Lee said the confidence of the U.S. side, who have had a rocky ride in recent years, would not be shaken.
"The last few years have been an up and down rollercoaster, we haven't really been on a good level but now we're at a high level," he said.
Italy were under pressure against Australia before coming back from the brink to win 21-25 18-25 25-21 25-14 15-13.
Earlier, Poland made the Earls Court volleyball arena their own as an army of supporters roared them on to a comfortable victory over Britain.
More red and white flags than Union Jacks were on show in the west London venue as the noisy Polish fans helped their team to a 25-16 25-19 25-18 triumph that secured a berth in the knockout stages.
The large Polish community in west London means the 1976 Montreal Olympic champions have been playing their matches as a virtual home team.
"We and Great Britain, we are on completely different levels, we've got different goals than they've got," captain Marcin Mozdzonek said, adding Poland's aim was to reach the final.
Britain's Jason Haldane said Poland, who have not won an Olympic medal since Montreal, were one of the favorites for gold.
"We don't really get a chance to play teams like this and you need to play teams like this to understand what you need to achieve and strive for," he said.
Making their Olympic debut, the home team have yet to win a set in the tournament after a tough few years of heavy funding cuts and a struggle for quality opponents in the build-up to the Games.
"We're doing this for the experience and the pride of representing Britain in the Olympics. Without the funding it's impossible to have a world class program," Haldane explained.
Elsewhere in Group B, Germany defeated Tunisia 25-15 25-16 25-16 to keep alive their qualification hopes.