Italy, co-helmed by Australian Jimmy Spithill, have clinched a four-second win over America's Cup challenger rivals Britain, levelling the series at 2-2 in an intense contest in top-of-the-range winds off Barcelona.

Earlier on Sunday, Luna Rossa Prada Pirelli had been forced to concede a win to Ineos Bri when they damaged the towering wing-like sail on their AC75 foiling monohull, just managing to get it swapped out in time to compete in the second race of the day.

"It was a fun one," Spithill said on the America's Cup live broadcast after Italy's crucial win, adding: "We've seen two evenly-matched teams go head-to-head.

"Probably the most frustrating part of the day was just the wind limit, but we did get the race off and from there the boys just bounced back brilliantly, especially after that unfortunate issue with the mainsail."

The two crews fought out a close match race, with Italy taking an early lead but pursued to the finish line by Britain with the AC75s at times touching speeds of 55 knots, spray streaming off their hydrofoils as they flew downwind.

"It was a tough one. It was a great race," said Britain's Ben Ainslie, whose team had several protests overruled by the umpires as the two boats sped around the course, their hulls humming in winds of around 20 knots.

"This is a joke, umpires," Ainslie's co-helm Dylan Fletcher said on the on-board communications system as the British tried to force a penalty on the Italians during one leg.

Racing will continue on Monday in the first-to-seven-wins Louis Vuitton Cup, with the winners getting to challenge holders New Zealand for the coveted America's Cup trophy.

Earlier, another of the huge foiling AC75s got into trouble, capsizing while out testing in the windy conditions. The Swiss team, who have been knocked out of the challenger series, said in a statement that all their crew were safe.

The Swiss boat was later towed back into port, with the hull low in the water as the pumps worked to empty it.