Team NZ and Team USA can't be separated for speed, leaving the America's Cup to be decided by sailing skill.

That's the view of Swedish syndicate team director Iain Percy, whose boat was eliminated by the Kiwis in the final of the challenger series in Bermuda.

Emirates Team NZ, who were beaten 9-8 in a memorable Cup Match four years ago, will resume hostilities in the best-of-13 final beginning on Sunday (NZT).

Team USA, who start with a 1-0 lead after winning the qualifying series, will be tough to beat, Percy predicts.

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The American defenders won both races against Team NZ in that series, with their charismatic skipper Jimmy Spithill later outlining some of the on-water mistakes made by Kiwi helmsman Peter Burling.

Percy says the Team NZ crew will need to refine their tactics in what is a very quick boat.

"It will come down to sailing, that's for sure. There won't be enough speed differences for one team to win without sailing well," Percy said.

"So I would say have real attention to detail and realise the details of each individuals' performances on the water will ultimately define the result."

An obvious area for Team NZ to improve is the start, with Burling having taken a conservative approach to most races in the challenger final.

Burling admitted he had backed his boat's speed and crew racing ability to catch the Swedes in a series they won 5-2.

Percy, a double Olympic champion for Britain, said accomplished fleet sailor Burling was still clearly learning match racing techniques in his America's Cup debut.

"Truth to be told it was quite a whitewash there (starts)," Percy said.

Swedish skipper Nathan Outteridge paid tribute to the designers at Team NZ, whose boat speed had seen off the other challengers.

However, the Australian wasn't convinced the Kiwis' much-heralded "cyclors" grinding system made the difference.

"I know everyone likes to talk about how magical the bicycles are - I've not sailed the boat so I don't know exactly how their boat works - but I don't think that was the main reason," Outteridge said.

"I think it comes down to more finer details of foil development and control systems and things like that."

-NZN