American challenger capsizes after horror crash while Ainslie stays unbeaten at America's Cup

US challenger American Magic suffered a horror crash, as a sudden gust of wind saw their boat sensationally flip, leaving officials frantically fighting to prevent a capsize becoming a sinking.

Dean Barker's crew had lost their first three races of the Prada Cup, a three-boat Challenger Series that will decide who takes on defending champions Team New Zealand for the America's Cup, sport's oldest international trophy.

They finally looked like putting a win on the board when leading heading into the final leg of their race with Luna Rossa Prada Pirelli, only for a gust to send their bow spectacularly shooting skywards.

Some of their 11-strong crew, who were quickly all safely accounted for, were sent flying into the water but it was a timely reminder of how dangerous this sailing can be, eight years after British Olympic champion Andrew Simpson died when his boat capsized during America's Cup training in San Francisco.

Coastguard, race officials and support crews from rival teams raced to save the stricken multi-million dollar boat, named Patriot, installing floatation buoys to keep it from sinking, with organisers activating their emergency management plans.

Meanwhile, Sir Ben Ainslie's Britannia remains unbeaten after riding the waves and their luck to continue their stunning start to this America's Cup campaign.

Team Ineos UK duelled with Luna Rossa Prada Pirelli in a fascinating tactical battle, with shifting wind conditions seeing the lead constantly change.

Their first race was abandoned and the Italian challenger took advantage of the restart, building up a 44-second advantage at the halfway point.

But with Olympic champion Giles Scott calling the savvy tactics, Ainslie's crew overhauled that lead and sailed away to bank a fourth win in a row - a remarkable turnaround after the boat had seemed so uncompetitive in the pre-Christmas warm-up regattas.

The top team after this first series of round robin races, which concludes next weekend, will progress straight to the Challenger Final, the winner of which will then progress to contest the 36th America's Cup.

No British boat has ever won the 'Auld Mug' and you need to go back to 1964 for the last time one contested it.