What was supposed to be the British star's voyage toward coronation as the greatest sailor in Olympic history has been interrupted by a remarkable performance by Denmark's Jonas Hoegh-Christensen in the Finn class.
So far, all Ainslie has seen of the Dane is the stern of his boat.
Hoegh-Christensen finished first and second in Tuesday's two races on a grey Tuesday afternoon with plenty of sea spray for a 10-point lead over Ainslie after six races. Ainslie had finishes of 4-3 as the 24-boat fleet sailed in winds that reached 17 knots.
Ainslie is trying to win his fourth straight gold medal and fifth games medal overall. If he wins gold, he'll supplant Hoegh-Christensen's countryman, Paul Elvstrom, as the greatest sailor in Olympic history. Elvstrom won four straight gold medals from 1948-60.
But Ainslie has yet to finish ahead of Hoegh-Christensen, who quit sailing for three years after failing to win a medal in Beijing and went to work for concert promoter Live Nation. On a leave of absence for the games, he's due back at work in two weeks, making sure that tickets are sold and there's beer in the concession stands.
Ainslie, the star of the well-funded British team who has a job lined up in the America's Cup after the Olympics, isn't ready to panic.
"Today was a much better day than yesterday," Ainslie said. "I was really frustrated yesterday. Today was much better. I was in the game. But at some point, I've got to start getting some points back."
In the first race Tuesday, the Dane posted his third wire-to-wire win in the regatta.
"I've done well before. I've always had the feeling that I could beat Ben on my best day, and I could beat all the other guys when I sailed my best," said Hoegh-Christensen, a smiling, unassuming 31-year-old. "I've been sailing my best here for the last three days. If I can keep that up, yeah, there's a good chance I can win. I don't know if I'm surprising myself. I'm a bit surprised it's going this well but I always thought I had it in me, and I guess I did."
Hoegh-Christensen is sailing so well that he was able to post the second-place finish despite a bad start. He thought he was over the line early and began turning back, but then noticed there was no individual recall flag flying on the committee boat, so he turned back onto the course. By then, he was behind, but he quickly closed the gap.
In the day's first race, he had a great start and led at every turning mark to win by 23 seconds over Zach Railey of the United States, the 2008 silver medallist who had his best finish.
Railey finished eighth in the second race and is 12th overall.
The Finns get Wednesday off.
"I'm an old man in this fleet and I definitely need the rest," Hoegh-Christensen said. "I gave it my all today. I had my lungs inside out when I crossed that finish line. I was trying to do my very best and push it as hard as I can. I definitely need the rest tomorrow, so, big steak and feet up, and ready for Thursday."
Ainslie, who's rallied in previous Olympics, also plans to eat well to get his energy level back up.
"There's still a long way to go," Ainslie said. "But he's sailing really well. At some point the table's got to turn."
Railey said Hoegh-Christensen has nailed practically every wind shift sailing upwind.
"Sailboat racing, everybody tries to make it so complicated. But all it is is going the right direction," Railey said. "Jonas is going the right direction on almost every beat. If it goes right, he's been on the right-hand side. If it goes left, he's been on the left hand side. He is sailing absolutely fantastic and if he keeps that up he's going to be very hard to beat.
"He might have taken the wind gods out for dinner before the regatta started," Railey added.
"He's certainly having the regatta of his life at the moment. Credit to him."
Ireland's Annalise Murphy continued her surreal run in the Laser Radial, winning her fourth straight race. She has three wire-to-wire wins and the worst she's been at any mark is second.
In the 49er skiff, Australian favourites Nathan Outteridge and Iain Jensen finished 2-4 to jump into the lead. They managed the fourth-place finish despite capsizing. Outteridge, who missed out on a podium finish in Beijing when he capsized in the medals race, is skipper of Team Korea in the America's Cup World Series.
In the venerable Star class, defending gold medallists Iain Percy and Andrew Simpson of Britain finished 1-2 to hold a four-point lead over Brazilian rivals Robert Scheidt and Bruno Prada after six of 10 races. Scheidt and Prada went 2-1 on Tuesday to jump from fourth to second overall.
The Brazilians beat the British by eight seconds in Race 6. On Sunday, the Brazilians prevailed in a photo finish against Percy and Simpson.
Four years ago, Percy and Simpson beat Scheidt and Bruno for the gold medal. The Stars are also off Wednesday.
In the Laser, Australian Tom Slingsby of America's Cup champion Oracle Racing went 2-6 to remain in the lead.
Anna Tunnicliffe of the United States, the 2008 gold medallist in Laser Radial who's the favourite in women's match racing, is tied for third in the round-robins.
Windsurfing opened Tuesday and Dorian van Rijsselberge of the Netherlands won both men's races. American Robert Willis went 7-10 for seventh place. Marina Alabau of Spain leads the women after going 2-1, while American Farrah Hall (22-18) is 21st.