Reigning Olympic champions Todd Rogers and Philip Dalhausser made a solid start in their attempt for back-to-back gold medals as they disposed of Japan in straight sets in Pool B.
The men's tournament favourites put on a workmanlike performance, underpinned by a typically dominant display on the defence by Dalhausser, as they posted a 21-15 21-16 win under the floodlights.
Meanwhile, counterparts Jennifer Kessey and April Ross made it two wins out of two for the US women's teams as they cantered to victory against Argentina's Ana Gallay and Maria Virginia Zonta in Pool D.
Italy's Paolo Nicolai and Daniele Lupo defied their tender years to claim an impressive victory over Switzerland's Patrick Heuscher and Jefferson Bellaguarda in the final match, while there were also victories in the men’s for Latvia, Netherlands, Brazil and Spain.
Brazil’s women began their Pool E campaign with a routine win against Netherlands. The South Americans were rarely troubled in the contest against Madelein Meppelink and Sophie van Gestel and eased to a 21-10 21-19 victory in just 36 minutes.
Maria Antonelli made the difference on the attack for the Brazilians with a total of 14 winning hits, while Talia proved a formidable barrier at the net, blocking five shots.
In other women’s games, Italy beat Russia while there were also victories for Spain, Germany and Host Nation Great Britain.