Great Britain's match racing team had to settle for silver at the World Championships as Anna Tunnicliffe skippered the US to victory.
Tunnicliffe, Molly Vandemoer and Debbie Capozzi beat defending champions Lucy Macgregor, Annie Lush and Kate Macgregor 4-0 in the final.
Macgregor was penalised in each of the first three races in Fremantle Harbour.
GB's John Pink and Rick Peacock lead the 49er class ahead of Australians Nathan Outteridge and Iain Jensen.
However, the Britons have seen their advantage cut to two points after finishing ninth and 15th in Friday's races.
"I did really want to stay with the fleet in a clear lane but we kind of got bounced from it," said Peacock.
"After that we thought the best way to get a clear lane was to split from the fleet and stay away from trouble, but not knowing that maybe shifts had a bigger input."
Fellow Britons Dave Evans and Ed Powys are seventh overall, with Dylan Fletcher and Alain Sign 15th in a class that still has a GB Olympic place up for grabs.
In the 470 class, Britain's Olympic selections Hannah Mills and Saskia Clark are fifth after eight races, with compatriots Penny Clark and Katrina Hughes in eighth place.
Tunnicliffe showed exactly why she is ranked number one in the world by guiding her team to a comprehensive match racing win over title holders Great Britain, despite the first three races being extremely close, with Macgregor struggling to make up for penalties in each.
Women's match racing will make its Olympic debut in Weymouth at next summer's Games.