The Melburnians had looked the more threatening side in attack at Allianz Stadium on Sunday, narrowly missing a handful of chances before Barbarouses broke the deadlock in the 81st minute.
Booed by Melbourne fans throughout, the former Victory forward had appeared Wellington's likeliest scorer and made good on a pass from Marco Rojas.
Barbarouses poked a left-footed strike past goalkeeper Jack Duncan from just inside the box and is now only four goals away from reaching 100 in the ALM.
The Phoenix celebrated before a jubilant, and surprisingly healthy, contingent of Wellington fans in the northern stand.
SCENES 🟡🔥 Wellington Phoenix win it in the 81st minute and the celebrations with the travelling supporters are elite!— Isuzu UTE A-League (@aleaguemen) Kosta Barbarouses the hero - a very cheeky finish against his former side 😮�💨 pic.twitter.com/0f4ITHZuLvNovember 24, 2024
"Fantastic to beat the team that was top of the table. I think the boys defended very well today," said Phoenix coach Giancarlo Italiano.
Victory had the chance to equalise from a free kick just outside the box in the final minutes of regulation time.
But Wellington goalkeeper Joe Oluwayemi, superb all afternoon, batted Bruno Fornaroli's strike away after the former Socceroo came on late as Patrick Kisnorbo's last roll of the dice.
"It's a hard one to take because I think we dominated for pretty much the whole game. They had one shot on goal, which was the goal," the coach said.
Phoenix players celebrate with fans after tasting victory at Allianz Stadium. (Jeremy Ng/AAP PHOTOS)
Victory fans were incensed when they were denied a penalty in the second half after Arzani fell in a challenge from Corban Piper and Hideki Ishige in the box.
"It's hard to tell from where I am (on the sidelines) if there was contact or no contact. I haven't seen it now but there's no point because it's finished," Kisnorbo said.
Arzani was substituted out of his first start of the season shortly after the no-call, appearing to have extended his left hamstring contesting the ball.
The 25-year-old endured a terrible run of injuries early in his career but Kisnorbo was confident his latest issue was not serious.
"It was just due to a cramp. It was hot and he hasn't been playing regularly," Kisnorbo said.
"But I thought he did well today."
The win consolidates Wellington's spot inside the top six and comes after eventual runners-up Melbourne Victory knocked the Phoenix out of championship contention last season.
