BARCELONA : Britain took the fight to Italy in their battle to become the challenger for the America's Cup on Wednesday, grinding out a win in a close-quarters contest to take a 5-4 series lead.

With both AC75 'foiling' boats bouncing around in choppy seas off Barcelona, British co-helm Ben Ainslie said they were on a "knife edge" trying not to come off their hydrofoils.

Italy were struggling with their choice of a smaller jib, Italian co-helm Francesco Bruni said after the race, the first of two on Wednesday in the first-to-seven Louis Vuitton Cup.

The winners of this series get to challenge defenders New Zealand for the coveted America's Cup later this month.

The British built on an early lead after a scrap between the two teams in the "pre-start", which is critical to getting a clean start and potentially crucial advantage, and capitalised on one bad tack by the Italians to extend their lead.