Europe's top-ranked beach volleyball duo Paul and Martin Laciga closed in on a last-16 spot with a win over Robert Nowotny and Peter Gartmayer of Austria.
Martin Laciga en route to victory
The Swiss brothers dominated the match, Martin opening with an ace and ending it with a servicer winner, to record a 21-14, 21-14 scoreline.
"We didn't play very well but they made a lot of mistakes," Martin reflected.
Nowotny said: "This is our first time in the Olympics but they have been in the top ranks for six years."
In other preliminary round matches, top seeds Brazil's Emanuel Rego and Ricardo Santos had to pull out all the stops to beat Norway's Iver Horrem and Bjorn Maaseide 21-15 19-21 15-10.
But Brazil's second seeds Benjamin Insfran and Marcio Araujo easily put away France's Stephane Canet and
Mathieu Hamel in straight sets.
In the women's tournament, American Misty May gave team-mate Kerri Walsh an ideal 26th birthday present with an routine victory over Japan.
May, whose fitness had been in question after two months out with an abdominal strain, came out fighting and the world champions quickly dismissed Chiaki Kusuhara and Ryo Tokuno 21-9 21-16.