Britons Hannah Mills and Saskia Clark had to be content with a silver medal after losing out in their final 470 shootout with New Zealand in Weymouth.
The two crews were already assured of a medal and shared the lead going into the winner-takes-all final.
But the GB duo were undone by a big wind shift on the opposite side of the course in the first leg and finished the medal race next to last.
New Zealand's Jo Aleh and Olivia Powrie won the race to clinch gold.
"The Kiwis have sailed well today and all week, as have the British pair and their heads are down but [they] won silver and they'll take a lot from that. They've sailed well and sailed maturely."
The Netherlands pair of Lisa Westerhof and Lobke Berkhout held off a number of boats to take the bronze medal.
"We just feel a bit gutted at the moment that we didn't put a big show," said Clark, who was sixth in the 470 in Beijing with Christina Bassadone.
Mills and Clark harried New Zealand in the pre-start but the Kiwis chose the right side of the course and made huge gains to lead around the first windward mark as the GB crew rounded in 10th and last.
"We had the Kiwis on the start line and felt like the left had better breeze but a shift came in to the right and it was game over," added Clark.
The light, variable winds meant the course to be shortened and Mills and Clark were unable to catch the Kiwis, who stretched into a big lead.
The Britons gained a place but Aleh and Powrie cruised home 41 seconds clear of Italy and almost two and a half minutes ahead of Britain, while the Netherlands came sixth to fend off France by a point for bronze.
Mills, 24, and Clark, 32, only paired up in February 2011 when the latter was left without a helm after double gold medallist Sarah Ayton retired.
The pair were World Championship runners-up in
Perth in December 2011
but then won the 2012 World Championships in
Barcelona in May.
"It's not going to sink in for a while, but it's pretty cool," said gold medallist Aleh. "Yachting's been struggling for a while at home and no woman has ever won a gold in a sit-down boat."