Britain and Italy have shared two closely-contested races in the America's Cup challenger series, leaving the first-to-seven event finely poised at 3-3 as they bid to take on defenders New Zealand for the 'Auld Mug'.

INEOS Britannia, co-helmed by four-time Olympic gold medallist Ben Ainslie, won Monday's first race but Luna Rossa, co-helmed by two-time America's Cup-winning Australian Jimmy Spithill, won the second to level.

With a stiff Mediterranean breeze off Barcelona below the maximum level of 21 knots for racing, both crews relished the high-octane sailing at speeds sometimes exceeding 50 knots on Monday.

The winners of the Louis Vuitton Cup get to challenge New Zealand for the 'Auld Mug', which dates back to 1851 and is known as the oldest trophy in international sport.

In the first race, INEOS Britannia capitalised on Italy's Luna Rossa getting caught by a momentary loss of control in their foiling AC75's rudder to rip across the start line and establish an early lead, which they defended to the end.

With close-quarter tack-for-tack engagement, Ainslie and Dylan Fletcher tried to slow Spithill and Francesco Bruni with 'dirty air' from their rig.

"They came back well ... They pushed us really hard. The guys did a good job to defend and keep the boat on its feet," Ainslie, 47, said of the tight contest.

The tables were turned in the second race, the Italian boat stamping their authority on their opponents to even the scores.

Bruni said the conditions had made for "very enjoyable" racing after the Italians dominated the second contest, sailing a near perfect race in their 'silver bullet', as their AC75 is known because of its sleek lines and metallic finish.