A thrumming yacht club hooted with glee as Emirates Team NZ zipped over the finish line in first place - winning two races in a row.
ETNZ now have an early 1-0 advantage over their archrivals Oracle Team USA in the America's Cup first-to-seven series off Bermuda.
The challengers quickly erased the defenders' one-win advantage on the scoreboard - a result of Oracle's win in the challenger qualifying series earlier this month - and built their own lead with victory in the day's second race.
Auckland man and keen sailor Malcolm Scott said the atmosphere was "fantastic" at the packed Royal New Zealand Yacht Squadron.
ETNZ helmsman Peter Burling's dominant display saw him get the better of counterpart Jimmy Spithill throughout the opening exchanges, winning both starts and overcoming slight lapses late in both races.
Both ACC (America's Cup Class) boats were even off the start-line in Race Two, but Team NZ built superior speed to the first mark and quickly extended to more than a minute in front at the third gate.
Oracle made huge gains up the fifth leg and were within a couple of metres, rounding the top mark, but immediately fell off their foils on a gybe and lost several hundred metres in the space of a few seconds.
That error cost the American syndicate any chance of overhauling their rivals.
Team NZ skipper Glenn Ashby said they made a few mistakes but it was a fantastic rally.
"It's so shifty and so puffy, as we saw out there ... you never stopped trimming something for the whole day, so those guys got an absolute whipping today."