Barrett's second try of the match came just two minutes after Wallabies centre Kurtley Beale had given his side a 29-28 lead and hope of keeping the trans-Tasman Bledisloe Cup series alive for the third game in Brisbane on Oct. 21.
The Wallabies, however, were left to rue some wayward kicking from flyhalf Bernard Foley, who left nine points on the field with four missed shots at goal at Otago Regional Stadium as New Zealand retained a trophy they have held since 2003.
"That's what the Bledisloe Cup is about," All Blacks captain Kieran Read said. "Two great nations fighting for it. We had to dig deep but those are the games, those little moments and I guess we just got one right at the end there.
"We are pretty proud at the moment."
Australia were hammered 54-34 in Sydney last week but provided a perfect response to their critics, racing out to a 17-0 lead that started with an 80-metre intercept try from Israel Folau inside the first 30 seconds.
Folau's score set the tone for the opening 20 minutes with the All Blacks dominating possession as the visitors showed far more discipline in defence and seized on what opportunities they had to punish the home side.
Michael Hooper then scored from an attacking lineout before Foley extended the lead with a breakaway try after the All Blacks had demolished a Wallabies scrum in midfield only for Will Genia to dart through a gap in the disintegrating pack.
The All Blacks settled and took control of the second quarter with Rieko Ioane touching down after clutching an inside pass from scrumhalf Aaron Smith following an attacking lineout.
Smith then burst over on the stroke of halftime after the All Blacks had won a succession of attacking scrums as the Wallabies led 17-14 at the break.
The home side, who had two tries disallowed by television match official Rowan Kitt, dominated the third quarter before Barrett scored his first try in the 60th minute.
The final quarter descended into a see-saw battle with Genia finishing a counter-attack that he had sparked before Ben Smith appeared to have given New Zealand the lead for good when he crossed in the 71st minute.
Beale, however, then gave his side hope of sealing the Wallabies' first victory in New Zealand since 2001 before Barrett completed a slick passing move to score his second try and dash Australian hopes.
"It was close to a fantastic performance," Hooper said. "We had full confidence to come down and win but New Zealand were too good for us."
(Reporting by Greg Stutchbury; Editing by John O'Brien)
