Nobody pours 10 years of their life – and millions of pounds of backers’ money – into a project that they don’t believe in. But right now, Ben Ainslie and his INEOS Britannia team will be digging deep into their reserves of self-belief.

The British America’s Cup Challengers are facing their final, most critical fight, with Emirates Team New Zealand driving home two dominant wins today to go 6-2 up. In the first to seven series, this is Match Point.

How the two teams respond to this final act will be fascinating. Both Ainslie and Burling are talking in the same terms of taking each race as it comes – but in reality, that means very different things for each of them. Racing is scheduled to resume tomorrow, though very light winds are forecast.

Brits making history

Ainslie, who told me before the regatta started that he was “quite happy being an underdog”, in truth would not have gone into this third Cup campaign without total confidence in his team’s potential.

History weighs heavily in the America’s Cup and the British had to achieve a greatness that has not been achieved in a century of sailing in order to take their place on the starting line alongside Emirates Team New Zealand this week. They were the first British team to qualify for the America’s Cup match in 60 years, and Wednesday’s double race wins were the first points scored by a British America’s Cup boat in 90 years.

But whilst what they have achieved is already exceptional, right now, they need to do something truly extraordinary in order to keep Emirates Team New Zealand, the most successful America’s Cup team in modern history, at bay.

INEOS Britannia racing on Day 5 of the Louis Vuitton 37th America’s Cup. Photo: Ricardo Pinto / America’s Cup

Both before and during this America’s Cup, Ainslie and the whole team have been utterly consistent in their view that they just need to keep improving, chipping away, making gains. But tonight they undeniably have their backs against the wall. Does this final act need them to find something beyond process and percentage gains – something more visceral, perhaps?

“I don’t think so. We’re not going to pull a rabbit out of the hat here. I don’t think anyone is,” Ainslie told me.

“It’s about this constant development. And I think we can sail faster tomorrow from what we learned so far through these finals, even though it’s very different conditions.

“We know the Kiwis are developing as well, and they got so much experience in the Cup and in these boats. And also we’ve got to go out and execute.”

Siege mentality for INEOS Britannia

Let’s not forget, Ainslie has been here before. He made his name in two epic dogfights against another Goliath of the sport – the legendary Brazilian Laser sailor Robert Scheidt in the 1996 and 2000 Olympics, famously getting the better of Scheidt in 2000.

He faced losing at his home Games to Danish Finn sailor Jonas Hogh-Christensen, at one stage lagging by 10 points, before surging back on a wave of outrage following an on-water protest call to take a record fifth Olympic medal, and fourth gold.

And he famously joined the afterguard of Oracle Team USA when they were 8-1 down in the 2013 America’s Cup before performing one of the greatest comebacks in sporting history.

“I’ve been in far too many sh*t fights in my career,” Ainslie observed today. “There were many scenarios, situations similar to this where it might appear pretty helpless, but actually you just never know what can happen.

“And what you’ve got to do is just keep digging and keep fighting. Like I said, you just never know what might happen.”

INEOS Britannia trailing Emirates Team New Zealand on Day 5 of the Louis Vuitton 37th America’s Cup. Photo: Ricardo Pinto / America’s Cup

What would have to happen, of course, is for the British team to not drop a single point, and stage a comeback equal to that in 2013.

“Yeah, it’s going to need to be something like that,” Ainslie said after racing today. “It’s 6-2 down. We’re on the back foot, we don’t have any second chances, but that’s the nature of the game.

“We need perfection from here on in. We don’t have any second chances, but in some ways that’s easy. You know what you’ve got to do.

“We’ve come a long way through this competition and improved a massive amount. You’ve just got to keep that going, it’s different conditions tomorrow. Why not come out, get a couple of bullets on the board?”

Casting back to the conversation we had in the weeks before the Cup, Ainslie had described the team as having “a bit of a siege mentality, which is never a bad place to be.”

Right now, INEOS Britannia are truly besieged. It’s a place he may be more comfortable than most – but can he and his team fight their way out one final time?