Britain's Olympic champions Helen Glover and Heather Stanning won the women's pair at the second World Cup meet in Aiguebelette, France.
They won in seven minutes 2.91 seconds to beat two American boats.
Stanning, 29, was competing at an international meet for the first time since she won gold with Glover, 28, at London 2012.
"It feels fantastic to be back. I knew it was in us, we just had to get out there and do it," said Stanning.
She returned to rowing last November after a six-month stint in the army, winning the British trials in April.
Great Britain had three other gold-medal-winning crews on Sunday, including London 2012 champions Andrew Triggs Hodge and Alex Gregory, in tandem with Moe Shihi and George Nash, in the men's four.
Graeme Thomas, Sam Townsend, Charles Cousins and Peter Lambert triumphed after catching the early leaders Germany in the men's quadruple scull.
And there was a GB one-two in the lightweight double scull as Olympic winner Kat Copeland took her first World Cup victory, alongside Imogen Walsh, with the emerging crew of Charlotte Taylor and Ellie Piggott surging to claim silver.
The third and final World Cup event takes place from 13-15 July in Lucerne with the World Championship following from 24-31 August in the Netherlands.