It took just three minutes for the Reds to open the scoring through Mileusnic before he grabbed a second soon after in clinical fashion to give United a commanding two-goal buffer.
The ex-Adelaide City forward then bagged his third, rounding off a slick attacking move involving Johan Absalonsen and Karim Matmour.
The Reds showcased immense maturity and composure to control proceedings on the uneven playing surface and were persistently dangerous in transition.
Adelaide quashed any hopes of a Bergers comeback after the interval when Mileusnic completed his treble in what was an extremely physical encounter.
Marco Kurz handed new signing Matmour his Adelaide debut, while Ryan Kitto was a surprise selection at left-back, as the German utilised a 4-3-3 formation.
3’ | GOAL! Mileusnic slides in at the back post, tapping home Kitto’s inviting cross to break the deadlock.
5’ | A melee breaks out after a strong challenge involving Jack Petrie and Vince Lia, following the former’s challenge on Absalonsen.
11’ | GOAL! Excellent work down the left side from George Blackwood finds Mileusnic, who shoots on the turn, to thump an emphatic half-volley past gloveman Christopher Theodoridis-Petropoulos.
Lovely work from Blackwood down the left hand side to cut the ball back to the winger, who thumps his shot on the turn past the 'keeper.— Adelaide United FC (@AdelaideUnited) September 13, 2017
49’ | Adelaide are quick in transition as Matmour is played in one-on-one with the goalkeeper though the Algerian drags his effort wide of the far post.
58’ | OFFSIDE! Jordan Wilkes scores a header off a free-kick, but the goal is correctly ruled out for offside.
61’ |GOAL! Mileusnic nets his third to score Adelaide’s maiden Westfield FFA Cup hat-trick, despite being unable to make clean contact on his strike. Absalonsen brilliantly picked out Matmour, who headed the ball across the face of goal and into the direction of the 24-year-old.
64’ | Blackwood smashed the upright before Mileusnic skied his follow-up attempt over the top of the crossbar.
79’ | Matmour has the audacity to attempt a rabona and agonisingly strikes the underside of the crossbar as it bounces out, in what would have been one of the greatest goals seen in the competition.
Wednesday, 13 September 2017
Westfield FFA Cup 2017 Quarter Final
Heidelberg United 0
Adelaide United 3 (Mileusnic 3’ 11’ 61’)
Venue: Olympic Village