United were 3-0 up inside 34 minutes of Saturday's match at Go Media Stadium in Auckland following goals to Riku Danzaki, Noah Botic and Hiroshi Ibusuki.
Matthew Grimaldi put the icing on the cake in the 87th minute as Western United, who beat Sydney FC 4-3 last week, moved into the top six.
It marked a remarkable plummet in fortunes for expansion side Auckland, who had posted wins in their first six ALM games before twice coming from behind to draw with Melbourne City 2-2 last week.
The Black Knights had conceded just three goals across 10.5 hours of action during their first seven games.
But that stingy defensive record was blown out the water as United cashed in with three first-half goals in front of 13,681 shell shocked fans.
Never change, — Isuzu UTE A-League (@aleaguemen) @WgtnPhoenixFC fans 🤣🤣Celebrating your rivals going behind, while at another game - now THAT'S commitment 😅� pic.twitter.com/InDjdp0ndIDecember 21, 2024
"It was our home game and our performance was so bad," Auckland captain Hiroki Sakai told Sky Sports.
"0-4 is such a disappointing result. I was so embarrassed. For this crowd, we have to give them three points for our next game."
Western United only had 39 per cent possession in the first half, but they were by far the dominant side as they unleashed 13 shots to five.
The visitors were gifted a penalty in the 16th minute following a handball in the box, and Danzaki made no mistake with the finish.
Auckland goalkeeper Alex Paulsen did well to block Ibusuki's close-range effort in the 23rd, but Botic was on hand to put away the rebound with an acrobatic shoulder-height swinging boot.
The home fans squarely blamed referee Casey Reibelt for United's third goal.
Reibelt got in the way of Jake Brimmer as the midfielder attempted to collect a pass in the centre circle.
With Brimmer unable to get to the ball, Tomoki Imai picked off the pass and raced forward before finding Ibusuki, who shook off a defender to nail his low strike.
Ibusuki makes it 3 for Western! 🔥— Paramount+ Australia (@ParamountPlusAU) @wufcofficial have stunned the ladder leaders with a flurry of first-half goals - as Hiroshi Ibusuki slots the visitors third for the afternoon#AKLvWUN is live on Paramount+ 📺 pic.twitter.com/uFsSJrjN9uDecember 21, 2024
Auckland were lucky not to be 4-0 down in the 43rd minute, with Angus Thurgate's half-volley from the edge of the box cannoning into the upright and bouncing away.
Thurgate was brilliant in the first half, with his creativity causing Auckland all sorts of problems.Â
Auckland coach Steve Corica took off Brimmer, Callan Elliot and Neyder Moreno in order to introduce Scott Galloway, Jesse Randall and Logan Rogerson for the second half.
The moves had an immediate effect, with the hosts creating a number of promising chances to give themselves hope of working their way back into the match.
United goalkeeper Matt Sutton pulled off some sharp saves to keep Auckland at bay, and Western struck at the other end when Grimaldi nailed his angled strike in the dying minutes.
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