At one stage, Oracle were 8-1 down to team Emirates New Zealand but a remarkable run of seven wins in a row has set up a thrilling climax to this prestigious competition.
Ainslie, who has won four Olympic gold medals in sailing, only joined Oracle in race six when the team were down 4-1 to Emirates and has played a huge part in their turnaround, says Pete Cummings.
"When Oracle went into the match and were losing all the races they just did not have the boat speed to match Team New Zealand who were a little more match fit having just won the Luis Vuitton," explained the SAP Extreme Sailing Team member.
"They took the boat back to the team base and did a full retune and re-optimisation of it and brought Ben on - those two factors together have really worked for them.
"Ben would have been in a tricky spot if he was on a slow boat but they have done such an amazing job getting the boat up to speed - it is arguably quicker than the Team New Zealand boat. I think he would have turned it around anyway because he is that kind of guy and is so solid with his tactics."
Cracking under pressure
Despite their brave faces, Cummings believes that Team New Zealand are battling with the pressure of expectation - especially having not been able to close the deal with such a huge advantage.
"New Zealand looked broken yesterday. I really feel for Dean Barker (their helm), he must be chewing up inside. He is one of the best sailors in the world but if he loses this match he will be known as a choker.
"He has had it on match-point for a week and has not been able to close it out. That must be tough and although in front of the media he is saying all the right things about belief, when he is sitting down alone it must be playing on his mind. Team New Zealand are such a national team - they are funded by the government and they have the weight of the country who have funded them for the best part of three years, so the pressure is massive on them."
It all comes down to one final race and Cummings says that now is not the time to try something new. Doing the little things right and holding your nerve is what will triumph - and for Cummings there is only man one for the job.
"I think the breeze is going to be up again and it is going to be full on. It is so late in the day that I think it is more of a risk to try and do something radical. They both have to go out and do what they have been doing - it is going to be a matter of attention to detail.
"Whoever wins this match is the team that goes into it with the strongest mentality and is able to hold their nerve. Neither team can afford to get flustered; they have to do all the little things right.
"I would never bet against Ben Ainslie in sailing - the tactician has the biggest pressure on the boat - he has to make all the right calls. You don't win four Olympic Gold medals by not being able to handle that pressure. He has got Tom Slingsby alongside him who is a current Olympic champion in the Laser class - so chances are when they make a decision at the back of the boat it is going to be the right one. We have seen Oracle win seven in a row and I just cannot see them not finishing the job."
Catch the final race of the America's Cup, 9pm, Wed, Sky Sports 2 HD