The first race in the contest to win the world's oldest sporting trophy was fought out on Bermuda's Great Sound by Oracle Team USA, skippered by Jimmy Spithill and Emirates Team New Zealand, helmed by Peter Burling.
Kiwi helmsman Peter Burling, 26, won both starts in the third and fourth races, as he had on Saturday, which has been a surprise against Spithill who is famously aggressive on the start line and has greater match-racing experience.
But the Kiwis came off their foils during a hard maneuver and slowed dramatically in light, shifty wind, losing half their lead.
In relatively light winds, Burling continued to sail smoothly, extending the Kiwis' advantage to a healthy margin of one minute and 52 seconds over their rivals by the fifth gate.
The Kiwi syndicate have won four-from-four races in the Cup Match off Bermuda so far, having started one point behind, and now need another four to clinch the Auld Mug.
Result: The Challenger won both races, but are only up 1-0 due to the convoluted scoring system that benefited the Defender due to their performance earlier in the qualifier stage.
Team New Zealand after their win in race number one.
"I think what happened is that we lost a rudder", revealed Spithill, reflecting on the manoeuvre that all but ended their challenge. Theyre going to be there when we need them..
However, a six-day break until race five and six on Sunday (NZT) will allow Team USA to make changes to a defence which is teetering.
Team USA skipper Jimmy Spithill doesn't believe the cyclors are the key to Team NZ's early advantage in the America's Cup final.
Spithill's Oracle team now face an uphill battle to win the 35th edition of the competition, where the trophy is earned by the first team to reach seven points.
Certainly Team USA will be operating from a position of strength in the decisive series.
As for Oracle's foil selection, "I thought we made a good step forward", Spithill said.
The always-crafty Kiwis are using a "cyclor" grinding system.
"I think it just shows that you guys will fall for anything", Spithill chuckled.
It is not so much that Oracle are losing but rather the manner in which they are being blown off the water, with Team NZ better in every department as they stormed to victory in race three and four by 49 seconds and 1m 12s respectively.