LONDON >> All four American teams — two in the men’s tournament and two in the women’s — finished the Olympic beach volleyball round-robin atop their pools, with defending gold medalists Todd Rogers and Phil Dalhausser beating the Czech Republic in the finale of the opening round today.

All four Brazilian teams also won their pools, setting up a potential collision between the sport’s traditional powers in the knockout round. Defending world champions Emanuel and Alison of Brazil struggled early but beat Italy’s Paolo Nicolai and Daniele Lupo 26-24, 21-18 to keep the four Brazilian teams unbeaten in 12 matches.

“They’re the strongest countries,” Rogers said after beating Premysl Kubala and Petr Benes 21-13, 21-15. “It’s holding up so far, I’d say.”

Thursday was the final day of the preliminary round. The top two teams in each pool advance, with the best third-place teams relegated to a lucky loser round later Thursday.

Americans Jennifer Kessy and April Ross finished 3-0 with a 21-19, 19-21, 19-17 victory over Spain. Kerri Walsh Jennings and Misty May-Treanor also finished their pool play on Wednesday with a 3-0 record and a No. 1 seed, and Jake Gibb and Sean Rosenthal did as well, despite a 2-1 record.

In all, the Americans were 11-1.

In other action, Martins Plavins and Janis Smedins of Latvia beat Reinder Nummerdor and Rich Schuil of the Netherlands in a matchup of unbeatens. Both teams advanced to the knockout round.

Spain beat Japan 21-19, 22-20, and Jonathan Erdmann and Kay Matysik of Germany beat Venezuela 20-22, 21-16, 15-11.

Marleen van Iersel and Sanne Keizer of the Netherlands beat Ana Gallay and Maria Virginia Zonta of Argentina. The Dutch advanced to the knockout round and the Argentines were eliminated.

Italy beat Canada to knock them out of the tournament and Germany beat Madelein Meppelink and Sophie van Gestel of the Netherlands in straight sets. Russia beat host Britain in straight sets to knock them out, too.

Maria and Talita of Brazil beat Becchara Palmer and Louise Bawden of Australia, 18-21, 21-16, 15-9.