"For us it’s all about resetting now and once we know the landscape of the league, it’s about signing players that are currently with a club and recruiting the right players to represent us," Wanderers' coach Jean-Paul de Marigny said.
That was a constant from kick-off for Wanderers, who conceded after just six minutes. Running on to the end of a perfectly weighted cross from United's Max Burgess, Josh Risdon prodded a header into the net from close range to put Western Untied into the lead in the sixth minute.
Wanderers goalkeeper Tristan Prendergast prevented Western United from doubling their tally shortly after when he blocked Burgess' shot from close range. However there was little Western Sydney's gloveman could do against Besart Berisha in the 19th minute.
Risdon narrowly beat the offside trap to supply a clever square ball to the oncoming Berisha, who made no mistake in slotting past Prendergast.
With the season slipping away, Wanderers forward Kwame Yeboah led their hopes of a revival by testing United goalkeeper Filip Kurto with a powerful shot from distance, before forcing a superb reflex save from the Polish goalkeeper minutes before the break.
Whatever stern words coach Jean de Marigny said during the break failed to breath life into the Wanderers. Instead, a moment of magic from United's Italian star seemingly killed their season.
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Dribbling inside from the corner flag, Diamanti spotted Prendergast off his line and punished the Wanderers goalkeeper with an audacious lob from an acute angle that flew into the corner of the net to make it 3-0.
Western Sydney did claw one back in the 69th minute through captain Mitch Duke, who steered a powerful header into goal before a breathtaking finish from substitute Tass Mourdoukoutas five minutes later. His back-heel finish left Kurto helpless but to watch the Wanderers make it 3-2 .
With 10 minutes remaining, their outbound captain did the unthinkable to draw level. Pouncing on a goal-mouth scramble, Duke powered a shot into the corner to square the ledger in 82nd minute.
However, parity was fleeting. A swift counter-attacking goal by Burgess put United back into the lead before yet another moment of magic from Diamanti sealed the three points that kept their season alive. The Italian playmaker struck another delicate chip over the head of Prendergast to make it 5-3 to consign the Wanderers to another season without finals football.