Oracle Team USA skipper Jimmy Spithill has described the next five days as the most crucial of his campaign, if his team are to retain the America's Cup.

It's not exactly the 8-1 deficit that he faced four years ago, but Spithill's Oracle team sit well behind Emirates Team New Zealand after the opening four races of the America's Cup in Bermuda.

After starting the finals on negative one, Peter Burling's Team New Zealand hold a 3-0 lead with four straight victories. Team New Zealand were once again dominant on the water today with a 49-second win in race three and a 1 minute and 12 second victory in the final race.

The two teams now have five days off before racing resumes. The first team to seven points will be crowned America's Cup champions.

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"I think it's pretty obvious these guys are faster and we need to make some serious changes," he said afterwards.

"Today, I thought we got off the line pretty well, but they were pretty impressive accelerating and certainly a lot of the transitions around the race track.

"Clearly, we need to now put everything back on the table. I think these next five days will be the most important five days of the campaign."

Spithill hinted his team would be working hard to improve the speed of their ACC boat, after barely firing a shot over the past two days.

"No two ways about it, we will look at every single thing we can. We've got an incredible team on the shore - boat building team, design, engineering.

"We've been here before, we've got five days to respond now and everything is up for grabs.

"Nothing will escape our eyes, I can guarantee you that ... whether its system related or appendage related, sailing technique, strategy ... we're going to look at everything."

"We've got a very, very good group up here and we feel with the resource we've got, we can make changes that are going to have to improve the boat and give us more speed.

"It looks like we've got some good sailing days coming up and we'll be on 24-hour shifts."

At the post-race press conference, Spithill was asked if he thought the Team NZ boat was "suspiciously fast" and he chuckled.

"It's no secret that they've got speed and are sailing well. There are a lot of things that go into boat speed, but like I said, this isn't our first rodeo.

"We've been in this position before and had less time before, so we've got five important days and we'll be using every single hour of them."

Spithill was also asked whether his team were "shell-shocked" by Team NZ's performance.

"The guys are disappointed, we wanted a race win today and we've proved we can win races against these guys," he said.

"We topped the qualifying series for a reason, but clearly these guys have made a step since that time. Now we've got an opportunity of five days to respond."

Spithill insisted the boats were still competitive in today's conditions - winds were 9-12 knots - and the learning curve on this sailing class was still "almost vertical". He even conceded he may copy some improvements off his rivals.

"No idea is out of the question," he said. "I think you sometimes learn the most when you look across the fence at your competitors.

"Certainly I've always found, when you go up against the best, that's typically what brings the best out in you and that's usually when you learn the most."