Mills and Clark (both pictured above) climbed from second into a tie for the lead with the Kiwis in the final two opening-series races.

Britain and New Zealand are on 33 points and, barring disqualification, cannot be caught for the top two positions, while the Netherlands are third on 52 points, with France three points behind.

Britain's Lucy Macgregor, Kate Macgregor and Annie Lush were beaten in their match racing quarter-final by Russia, who now meet Spain the semi-finals, while Australia will race Finland, who beat the pre-event favourites, the United States.

"Like loads of kids, when I was 10 my dream was to go to the Olympics and be a medallist," Clarke said.

"To have that – and have a chance of a gold one – is awesome."

The Britons came eighth and second in their final two races as New Zealand's Jo Aleh and Olivia Powrie had a second and an 18th, which became their discard.

New Zealand's Jo Aleh and Olivia Powrie compete in the women's 470 sailing competition at the London 2012 Olympic Games

Mills, 24, and Clark, 32, only teamed up in 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.

The Macgregor sisters and Lush, who struggled in the round-robin section to qualify as seventh seeds, went into day two level with the Russian crew of Ekaterina Skudina at 1-1 and went 2-1 up after dominating Wednesday's opening race.

They were leading within 100 metre of the finish in the fourth match before Russia outmanouevred them to win on the line and went on to win the deciding match.

"I let the others down there at the end, it's gutting," said Lucy Macgregor.

"It feels like a massive missed opportunity but we really raised our game in the quarter-finals and we will be proud of this in the days to come."

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