United States challenger American Magic had its first loss but stayed atop the leaderboard after the second day of racing Friday in the America's Cup World Series off Auckland, New Zealand.
American Magic, backed by the New York Yacht Club, won one and lost one of its two tight races against Italy's Luna Rossa, ending the day with a 3-1 record.
The most aggressive racing of the series so far saw four penalties dispensed -- three against Luna Rossa and one against American Magic -- for rule breaches in pre-start maneuvering.
Defender Team New Zealand, which lost to American Magic in the second of two races on Day 1, joined the United States team at the top of the leaderboard with back-to-back victories over Britain's INEOS Team UK.
The British team had a much better day Friday than on a disastrous opening day when it battled major equipment malfunctions and was forced to retire from its second race.
Earlier Friday, helmsman Ben Ainslie blamed a system supplied by defender Team New Zealand for the technical problems that hampered his British team in the lead-up to sailing's America's Cup.
INEOS Team UK had breakdowns in both of its races Thursday on the first day of the World Series and was forced to withdraw from the second race when a battery failure left the yacht Britannia dead in the water.
There was doubt it would be able to race Friday, but after overnight repairs, it headed to the race course early to work out any lingering problems. Team UK completed both races against Team New Zealand, losing by margins of 1 minute, 32 seconds in the first race and 1:42 in the second.
But it showed an ability to compete when mechanical issues don't intrude. In the second race of the day, Ainslie pulled off a brilliant start move, leaving the New Zealand boat off its foils and gaining an early lead of almost 400 meters.
Team New Zealand regained the lead on the first downwind leg and showed better boat speed, but the British team was happy with its day.
"It was much better than yesterday," Ainslie said. "At least we got around the course, everything was working as it should and the guys did a really good job."
The day was peppered with dramatic incidents. In the first race, Luna Rossa incurred a penalty for entering the start box early and was forced to allow American Magic at least a two-boat-length lead off the line.
The American crew members had their hearts in their mouths when they put in a bad tack on the first beat, taking too long to lift the windward foil arm and causing the yacht Patriot to heel over dangerously.
Luna Rossa took the lead held narrow advantages for the rest of the race, winning by 12 seconds.
New Zealand had two nervous moments in its first race against Team UK. It came too close to the top mark after the first leg and at the bottom mark, the New Zealand boat Te Rehutai reared up on its foils, then crashed back after a jibing error.
"We made a bit of mistake and made life hard for ourselves," New Zealand helmsman Peter Burling said.
The pre-start of the second race between American Magic and Luna Rossa was full of action. The Italian team again was early into the box but offset that penalty when it gained right of way and luffed its rival.
American Magic helmsman Dean Barker then trapped Luna Rossa's James Spithill in a right-of-way incident that saw another penalty against the Italian team.
Thursday's variable wind conditions gave an early indication of the tricky conditions teams likely will encounter when America's Cup racing begins officially next year. The World Series is not part of the Cup regatta, which begins with a series in January and February to find the top challenger.
The World Series will be the only warmup regatta prior to the start of the 36th America's Cup in January. The Prada Cup for challengers will run Jan. 15 to Feb. 22, with the winner advancing to face Team New Zealand in the America's Cup match March 6-21.