Great Britain women's pair Zara Dampney and Shauna Mullin came from a set down to beat Canada in their opening Olympic match at Horse Guards Parade.
Dampney and Mullin lost the first set 21-17 but claimed the next two sets 21-14 and 15-13 to win their Group F tie.
"It was amazing," said Dampney. "We just wanted to relax, enjoy it, play volleyball the way we know we can, and I don't think I'll ever forget it.
Mullin added: "To win tells people we're here to do something."
In the day's other Group F match, Italy beat Russia 2-1.
In the men's group matches, Brazil almost suffered a shock defeat.
The number one-ranked pair Emanuel Rego and Alison Cerutti needed three sets to beat Austria.
Austrian duo Clemens Doppler and Alexander Horst are ranked 31 places below Brazil and eventually lost 19-21 21-17 16-14.
Netherlands were also given a tough time by Olympic debutants Venezuela before winning in three sets.
Spain eased to a 2-0 victory over Czech Republic, while Latvia came out on top of a close contest with Germany as they won 2-1.
Favourites United States brushed Japan aside in straight sets.