Ben Ainslie needs five of the best while 49er pair lose time after capsizing

Great Britain’s 49er class crew Stevie Morrison and Ben Rhodes capsize in Weymouth Bay yesterday (EPA)

A career-defining effort, with five days to rewrite the history of Olympic sailing, faces Britain's Ben Ainslie after the Danish threat from Jonas Högh Christensen yesterday raised another doubt about what had been seen as Ainslie's unquestioned supremacy.

Ainslie, winner of three golds in a row after an initial silver in 1996, lies 10 points behind the Dane after six races, never having beaten him once in a series in which he started as hot favourite.

Christensen seems to be enjoying a charmed life, even managing to turn back when he thought he had started the second race of the day prematurely and then ended up second, one place ahead of Ainslie. But Ainslie is unlikely to see his own desire for a fourth consecutive gold destroyed without first doing everything to bring Christensen's dream week to an end.

Both agreed that, with four more races to go before the double points top 10 finale, there was a long way to go. Both agreed that Christensen's 10-point cushion could vanish in a couple of bad races.

Ainslie said, before going into a day off today, that Christensen was having the regatta of his life. At the end of the first day he had said that "it is too early to start playing games" with Christensen. These two have not always had a friendly history. Both have a fiery temperament. It is not too early to start playing games any more.

Even managing to enjoy the pressure was Ainslie's long-time friend Iain Percy. After his opening race 11th is discarded, his record at the top of the score sheet is second, third, second, first and second, but that gives him only a four-point margin over the arch-rivals Robert Scheidt and Bruno Prada of Brazil.

Another old rival, but often training partner, Freddie Loof of Sweden with crew Max Salimen are a further three points back, but these three are significantly clear of a peloton led by Elvind Melleby of Norway and Mateusz Kusnierewicz of Poland.

There was more grief for Britain's 49er pair, Stevie Morrison and Ben Rhodes. "We were sailing the boat really nicely, sailing really fast, but we ended up in a really tight situation and I knocked Ben over like a skittle and that was that, we ended up getting a bit wet," said Morrison after they capsized.

Whereas the 49er favourites, Australia's Nathan Outteridge and Iain Jensen, recovered quickly from Outteridge being knocked overboard, Morrison and Rhodes dropped from fifth to finish 18th after their capsize. They, too, need a run of top results to give themselves a medal chance, even though they have 16 races left.

A second in the final race of a breezy day – even more wind is forecast for today – slightly improved defending gold medallist Paul Goodison's campaign in the Laser; two seconds for Alison Young in the Laser Radial lifted her to fourth in a fleet led by a so far unbeaten Annalise Murphy of Ireland.