The opening stages saw Wanderers striker Mark Bridge threaten on several occasions, but he was unable to break the deadlock, with his best effort going off target after being pushed wide by a defender.
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However, soon after the restart, Wanderers had the lead when Castelen whipped in a cross for Bridge to provide the finish for his fourth goal of the campaign.
Midway through the second half, Andreu hit the crossbar with a clever effort, but 11 minutes from time, the points were wrapped up when Castelen burst forward before his strike found its way past Danny Vukovic in the Melbourne net.
While Wanderers go clear in first place, Melbourne remain in third, six points behind today's opponents.