In his first full season as Melbourne Victory manager, and just his second year in charge of the club, Muscat guided Melbourne Victory to an A-League premiership-championship double in 2015, the Victory's third A-League premiership-championship double. Under Muscat, the Victory finished with a regular season record of 15 wins 8 draws and 4 losses, with a final points tally of 53 points, three points ahead of second placed Sydney FC and a final goal difference of +25, the highest of any club that season. Muscat guided the Victory to a 3–0 win over Melbourne City in the semi-finals, before recording a 3–0 win over Sydney FC at AAMI Park.