Sir Ben Ainslie urged his flying team to keep grounded as Britain's America's Cup challenge remained unbeaten in Auckland.

With American Magic out of the round robin racing after last weekend's spectacular capsize, Ainslie's Ineos Team UK needed one win over Italian rivals Luna Rossa to book their place in the Prada Cup final, the winner of which progresses to the 36th America's Cup match with New Zealand.

They suffered a major technical hitch before the start but still claimed a thrilling close quarters victory in a race that saw the lead change hands on nine occasions, Britannia hitting a top speed of 50 knots in shifty conditions.

"That was one for the fans and pretty awesome to take part in with lots of lead changes and neck and neck all the way to the line, it's certainly one of the best races I've ever been involved in," said Ainslie, a four-time Olympic champion.

"We had a few issues and were missing one of the key settings for the power of the boat, which really put us on the back foot. We didn't panic and the guys did an awesome job getting us around the track in one piece. It was a fantastic showcase for the sport."

Luna Rossa will now face American Magic in a best-of-seven repechage regatta for right to take on Ainslie in a head-to-head showdown to claim this challenger series, something no British boat has achieved since 1964.

Ainslie's reward is a prized three weeks off the race track to make further improvements to his boat, which just a few weeks ago looked the most sluggish of the challengers but has suddenly become the one to beat.

With this first phase of the challenge successfully completed, Ainslie has made the decision not to contest a dead rubber clash with Italy on Sunday with focus switching from the racecourse to the boat shed.

"British boats have always struggled with the America's Cup, it started in 1851 around the Isle of Wight and we've never won it, so we aren't getting ahead of ourselves," he added.

'We need to keep focussed and get our head down and make the most of this opportunity to make some more gains.

"We've got a list of upgrades we'd like to make and we've got a little bit more time to make some bigger upgrades now. We are just trying to get faster, you need constant improvement to win the America's Cup.

"We're happy to have won a few races but we know we'll need to get a hell of a lot better to win this thing."