He had been called in as an emergency replacement on-board tactician to salvage American pride, and the millions of dollars lavished by American software billionaire Larry Ellison on the giant catamaran carrying his company's name, Oracle. A worldwide audience was able to listen in as Ainslie implored the crew to "work your arses off".
Ainslie is the undisputed king of British yacht racing, his status as a team leader confirmed emphatically after a solo career where he captured four Olympic golds. Unforgiving on the water, he is a model of modesty on dry land.
"In other sports, good results would lead you to becoming a household name and whatever comes with that, but to be honest I'm quite comfortable with not being widely known," he says, reclining in the Royal Ocean Racing Club in St James. "I'm quite a private person and wouldn't really love the attention given to, say, a footballer."
The America's Cup is the oldest international sporting trophy in existence, named after the American schooner that won it in 1851.
The silver ewer was bought by the 1st Marquess of Anglesey for the Royal Yacht Squadron, and was initially known as the One Hundred Pound Cup. Legend has it that, as the America ploughed to victory past the Royal Yacht, anchored in the Solent, Queen Victoria, searching in vain for the trailing field, asked her attendant to identify the vessel in second place. "Your Majesty, there is no second," came the reply.
Donated to the New York Yacht Club, the rechristened trophy remained on the far side of the Atlantic for more than a century, the object of duels between successive generations of super-yacht. British contenders came and went, all unsuccessful and many complaining of unsporting behaviour by the hosts - the holder of the cup writes the rulebook.
"The Americans did a pretty good job of subtly manipulating the rules to make sure that it was almost impossible for anyone to beat them," Ainslie says.
American domination ended in 1983 when Australia II, equipped with a revolutionary winged keel, wrested the Auld Mug.
A yachting arms race ensued, with money and technology poured into ever more advanced designs. Ellison's involvement has taken the event to new levels but also threatens a monopoly - few can match his resources and commitment.
"Larry has taken a lot of criticism for this event," says Ainslie, "but I know his vision is to reduce costs and in the future to bring in more teams."
Like his skipper on Oracle, Ainslie was equipped with a screen on his arm relaying information from sensors strewn around the 72ft catamaran. So, was it British tactics or American technology?
"We'll never know," he offers. "I was a bit embarrassed about some of the comments made over here about me single-handedly turning the whole thing around. Not only are there 11 guys on the boat but a huge number of people on shore. It's like working with a Formula 1 car."
He pays tribute to John Kostecki, the American he replaced as tactician, for behaving in a gentlemanly manner, continuing to offer advice despite his eviction from the boat.
"I don't think John was necessarily doing anything wrong. The mood was obviously difficult because of the dire situation, so to bring in someone with a fresh perspective was a way of lifting the team. I did try to be super-positive but I'm not stupid enough to think I could do it on my own. As for technology, these boats are still so physical."
And dangerous, promising speeds of up to 43 knots. Ainslie was among those who pressed for improvements in safety following the death of his friend Andrew Simpson, killed when Artemis capsized.
Ainslie was born in Cheshire but moved at an early age to Cornwall. A skin condition led to him being bullied at school. Sailing provided an escape. "I didn't really enjoy school," he says, "but through sailing and getting results - it's amazing what it does for your self-esteem."
His father was crucial in forming his ambition.
"There was a pub a mile up the creek from where we lived which was our local, and it was Christmas morning and my dad said the family were going there and I should get in my boat and meet them. I was in my duffle coat with no lifejacket or anything like that, and it was the first time I'd sailed any boat on my own. You couldn't do it these days - social services would be all over you - but I made it. When you are out there on your own, all of a sudden you are in complete control."
A will to escape, yes, but the will to win?
"There was quite a telling moment in my childhood when I was sailing in a club race, and my parents had always been really supportive but never pushed me or anything. There was this race and I wasn't doing very well and sort of gave up. I was 12 years old or something. I didn't realise that my dad was watching. He came over afterwards, really pissed off.
"He said, 'If you want to go sailing for fun that's fine, that's great, but if you want to go racing and you are expecting us to travel around the country, then you've got to take it seriously, because I'm not going to waste my time.'
"It really sank in. I thought, 'He's right.' If you are going to do something seriously then you've got to give it everything."
The next Cup will be held in 2016 or 2017. Ellison wants to turn it into a truly global event, limiting expenditure, possibly, to attract a bigger field of 10 boats or more.
"There's an argument for fleet racing in this type of boat," says Sir Ben. "It has to be tried and tested but it would be an amazing spectacle."
Sir Ben hopes his success will spur British business to back a truly British bid for the Cup - British boat, British crew. Britannia will eventually regain what is rightfully hers, he believes.
"It's not a matter of if, but when," he promises. "As for me, I have about 10 years left at the highest level."
But of course he'll be there. Who could keep him away? Nobody calls Sir Ben Ainslie "nobody" and gets away with it.
