Britain’s Ineos Britannia piled the pressure on Italy in their fight to be challenger for the America’s Cup on Wednesday, clinching two tight races over Luna Rossa in “knife-edge” sea conditions to go within one point of winning the first-to-seven Louis Vuitton Cup series.

Against the backdrop of huge Italian and British flags flying over their bases in Barcelona, both AC75 foiling boats were bounced around in choppy seas, hitting speeds of more than 50 knots at times in a stiff Mediterranean breeze.

“It’s great, good effort from the team. It’s bloody hard to sail these boats in these waves,” Ben Ainslie said after the second win, which took Britain to a 6-4 lead.

The winners of this series challenge the holders, New Zealand, for the America’s Cup when the races start on 12 October. “Still a long way to go, still got to get to seven,” said the 47-year-old Briton.

Ainslie’s crew survived one scare when their boat touched down into the water before recovering its flight, giving the Italians a chance to get back into the race, but then managed to defend their lead, speeding downwind on the course.

“We’ll come out the next day swinging,” said Italy’s co-helm Jimmy Spithill, who acknowledged a strong sail by the British. “We just couldn’t get enough to get an overtake.”

In the first race, Britain built on an early lead after a scrap in the pre-start, which is critical to getting a clean start and potentially crucial advantage, and then capitalised on one bad tack by their opponents.

During the second, the teams were neck-and-neck off the start, with Britain building an early advantage and controlling the race with calm communication between Ainslie and his co-helm, Dylan Fletcher, as they watched out for rogue waves.

Britain’s cyclor, Neil Hunter, said: “We had significant sea state which makes a massive difference for us cyclors as the power demands are much more. Every function on the boat is being used twice as much so it was flat out today. It was pretty relentless but we did a good job of delivering the power when it was needed.”