Great Britain's Ben Ainslie said he is "back in the game" but admits he has a fight on his hands if he is to win a fourth Olympic sailing gold medal.
The 35-year-old climbed to second, 10 points behind Jonas Hogh-Christensen of Denmark, after a fourth and a third place on another windy day in Weymouth.
Ainslie is still yet to beat surprise leader Hogh-Christensen, who came first and second in the day's two races.
Ben Ainslie's Olympic record
There are four races of the opening series left to sail.
Ainslie came into the Games as many people's idea of a certainty for gold, but Hogh-Christensen is intent on ruining the Briton's quest to usurp fellow Dane and four-time gold medallist Paul Elvstrom as the most decorated Olympic sailor.
"I was really angry and frustrated yesterday, but today I was back in the game," said Ainslie, who has won three golds and a silver at the Games.
"Jonas is sailing really well, he's having the regatta of his life. All I can do is keep pushing hard and hope he slips up along the way. It's still a long way to go but at some stage I've got to start getting some points back."
Hogh-Christensen, who will go back to his job as commercial director of a concert promoter in Denmark after the Games, said: "I've always had the feeling I could beat Ben on my best day.
"If I can keep that up, there is a good chance I can win. I'm a bit surprised it's going this well, but I always thought I had it in me."
Britain's defending champions
tightened their grip on the Star class to lead by four points from Brazilians Robert Scheidt and Bruno Prada.
"All we can do is paddle to the end," said Percy, who is the oldest member of the British squad at 36. "We are definitely here to defend our title but it is going to be a fight to the end."
who is defending his Olympic Laser title, was in tears because of a back injury that is threatening to end his regatta.
"Hogh-Christensen's speed is a surprise to everyone, but Ben is still going quite well. His speed was good today.
"He would have been worried about his upwind pace yesterday but today he had great upwind pace, apart from Jonas. That is a little bit of a worry but Ben is rock solid. He won't be unnerved by it, he'll just be wondering what he can do, how he can go a bit faster.
"I never underestimate Ben. It's been a long time since I've seen him lose anything, even when things have gone terribly wrong in the beginning."
Despite climbing into 12th place overall with a 16th and a second, Goodison trails runaway leader Tom Slingsby of Australia by 40 points with the worst result to be discarded.
In the RS:X windsurfing classes,
opened his campaign with a fifth and a seventh for fourth overall, while Bryony Shaw had a seventh and a sixth to sit in sixth.
Weymouth local Dempsey, who won bronze in Athens but came fourth in Beijing, said he was "slightly disappointed" with his first day as he chases the gold that has eluded him in his three previous Games.
"It's steady. I haven't thrown it away, I'm still very much in the competition," said the 31-year-old, who is married to two-time Olympic champion Sarah Ayton.
British 49er duo
scored a third in their first race of the day but capsized in race two and finished 18th to remain 12th overall.
Morrison was upbeat despite his impromptu swim, pointing out the unpredictability of the class given that leaders Nathan Outteridge and Iain Jensen of Australia also capsized.
"There are an awful lot of positives out of a fairly major negative, but we're going very fast and for 99% of the time we're sailing very well," he said. "You can't win a sailing event by panicking. Equally, there's no denying the fact we've got a lot of work to do."
22, posted two seconds on day two to lie fourth behind Ireland's Annalise Murphy, who has won all four races.
In the women's Elliott 6m match-racing class, Britain's team of
won twice to sit in a tie for third in the round-robin stage.