Sydney coach Steve Corica has promised changes while ruing lapses of concentration, with Wellington's perfectly executed game plan carrying them to a 3-1 A-League boilover away win.
The Phoenix scored three first-half goals in 17 minutes on Saturday at Sydney's Jubilee Stadium, with striker Roy Krishna bagging a brace, to help Wellington coach and former Sydney FC captain Mark Rudan enjoy a memorable win over his old club.
Defender Michael Zullo pulled a goal back in the 89th minute, but Sydney suffered successive home losses for the first time since April 2016.
It was Wellington's first win since the opening round and their first over Sydney in seven games, having picked up just one point in their previous eight away matches against all comers.
Sydney's defence was caught ball watching in a nightmarish first half as a series of passes and crosses cut them apart.
Krishna raced onto a perfect through-ball from Sarpreet Singh in the 21st minute and outpaced Zullo and Jop Van der Linden before slotting it past Sydney goalkeeper Andrew Redmayne.
He scored again seven minutes later when he ran onto a Mandi through-ball and shook off Zullo.
"The first-half performance wasn't good enough. We got caught out way too many times,'' said Corica, who had warned his side about Wellington's pace and direct style.
"It's concentration - the first two goals were simple mistakes."
Central defender Steven Taylor completed Phoenix's first-half blitz when he was able to get in ahead of van der Linden to head home a Liberato Cacace cross in the 38th minute.
"We wanted to press them high," Rudan said.
"Both of Roy's goals were exactly the same and we worked on the training pitch to try and open them up exactly the same way."
It might have been a different story had Sydney's normally efficient goalsneak Adam Le Fondre not squandered a golden opportunity in the 14th minute.
Le Fondre was off target from close range after a fine cross to the near post by Paulo Retre.
Sydney captain Alex Brosque came close just before halftime when his shot was hacked clear by Taylor, with Phoenix goalkeeper Oliver Sail off his line.
Corica made a change at halftime, replacing Retre with marquee Siem de Jong, the Dutchman playing for the first time in five rounds after a hamstring injury.
De Jong had a shot pushed away by Sail in the 57th minute and the Phoenix survived some penalty-area scrambles and VAR reviews before Zullo's consolation goal.
"There will be some changes next week," said Corica, with de Jong in contention to start Saturday's derby against Western Sydney if he pulls up well.