Billed by Oracle Team USA's Jimmy Spithill as the "decider", the US skipper forced a penalty on New Zealand helmsman Peter Burling at the start of their race and built an early lead.
Groupama Team France, the pre-event underdogs, have struggled to get their 50-foot foiling catamaran to "fly" as well as the other five crews in the regatta, but in the light breeze Ainslie's crew fared no better.
Flying into the top mark on port at speed, Burling managed to cross the Americans who were on starboard and briefly took the lead.
The proximity to Team USA may also give Barker, who was dramatically beaten in the America's Cup in San Francisco by the US, better insight than anyone into the defender's weak spots.
In the first round robin, Oracle beat Team New Zealand by six seconds.
The four teams are vying for the chance to take on two-time defending champions Oracle Team USA in the 35th America's Cup Match that starts on June 17. "But at the end of the day it's about carrying on improving and carrying on learning and making sure we get back facing them again". The schooner America won the first race and the trophy was subsequently renamed the America's Cup.
In addition to the New Zealand-USA showdown, Saturday's last day of round robin racing will feature Ben Ainslie's Land Rover BAR taking on both Japan and Oracle and Artemis taking on France.
Ben Ainslie's British sailing team have earned a place in the America's Cup challenger play-offs in Bermuda but there are still worries about their performance following the first round of racing.
"We were really happy with the start", Artemis Racing skipper Nathan Outteridge said in a televised interview following his crew's victory over Oracle Team USA who remained on seven points, level with the New Zealand team.
The result means the US team will have a point lead against whoever gets to challenge them in a head-to-head match, which will be won by the first team to get to seven points.
The New Zealand team will be looking to bounce back quickly from yesterday's demoralising loss to Team USA.
After Saturday, Oracle will train on its own while the challengers sail their semifinals and finals.
The Kiwis also beat SoftBank Team Japan by 51 seconds, staying on their foils 99.6 percent of the time.
Team NZ were ruled to have crossed the race boundary, incurring a two-length penalty.
That heavy defeat put more pressure on the clash with France - who had lost to SoftBank Team Japan by nearly six minutes in the day's opening race - but Britain crossed the finish line just ahead of their opponents to avenge Monday's defeat.
