Despite the rhetoric, Oracle Team USA may struggle to improve their boat enough to turn around a 3-0 deficit in their America's Cup defence against Team New Zealand.

But veteran commentator Peter Lester has hinted that a line-up change may be needed, if the holders are to stage a comeback off Bermuda.

The Kiwis completely dominated on the Great Sound this morning, adding two wins to their 1-0 advantage overnight in their quest for the seven points that see them raise the Auld Mug.

A quirk in the scheduling now sees a five-day lay period until next Sunday (NZ time), a built-in opportunity for Oracle to turn their fortunes around after four successive losses.

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Skipper Jimmy Spithill is adamant the contest is not over and, remember, he masterminded a comeback from 8-1 down and the brink of defeat against Emirates Team New Zealand in San Francisco four years ago to retain the trophy.

But Lester, a former Team New Zealand tactician and Yachting NZ high performance manager, doubts there is much the American syndicate can do to structurally improve their ACC boat this week.

"The big difference from San Francisco is that a lot of the componentry is one-design, whereas in San Francisco, it wasn't," he said on today's Vodafone NZ Dockside show.

"They're really limited in what they can do in terms of the foils - I'm talking about daggerboards, daggerboard tips, rudders and elevators.

"Even the hydraulic control system for the wing, which is complex ... they're pretty limited in what they can do with that, because of their grinding power.

"The biggest gain for them will be in terms of having a look at what Emirates Team NZ are doing and then trying to replicate what they're doing on the water. I expect to see them on the water a bit, because I don't know, workshop time, whether they can make the massive changes that we saw in San Francisco.

"For sure, on the water, they can replicate what they've seen from Emirates Team New Zealand and try to get up to that level - it's a steep hill."

Lester warned that Oracle had plenty of resources and "smart people" to tap into, before they resume battle against Team NZ.

"They've got a guy over there called Grant Simmer [chief operating officer/general manager], who's been around this game forever," he said. "No-one knows better - you never hear of him, but believe me, he is one smart, cunning operator ... and so is Russell Coutts.

"At this point, in San Francisco, they made a big crew change, with [Ben Ainslie] hopping on for John Kostecki. In a six-man crew, who could they swap in and out?"

Vodafone NZ Dock In Show - Day 18

3-0 to #ETNZ, but there is no resting yet. Martin & Peter are live for the Vodafone NZ Dock In Show talking about the big week ahead.

Posted by Emirates Team New Zealand on Sunday, 18 June 2017

Lester credits Ainslie's introduction for a philosophy change that drove Oracle's historic comeback from matchpoint down and hinted this kind of change may be required again.

"I'm not suggesting that Spithill would be replaced at all, but [tactician] Tom Slingsby could be one of the keys to the door for Oracle. Slingsby and Kyle Langford, who is trimming the wing ... whether they reposition on the boat, we'll wait and see."

Lester was adamant Team NZ should continue doing their own thing and not spending too much time watching their opponents.

"There's still speed left in the tank for Emirates Team NZ and I'm astonished at the level of improvement, without substantial changes to the boat. They're just sailing the boat better and smarter.

"They are learning the detail to sailing their boat better and Burling is a quick learner - he's won four starts.

"For Oracle to win, Spithill has to get to mark one ahead of Buring and it hasn't happened yet."