Western Sydney Wanderers have booked their place in an A-League Grand Final for the third time courtesy of a 5-4 victory over Brisbane Roar.

In what turned out to be an epic encounter at the Parramatta Stadium, it seemed that visiting Roar were destined for a spot in next weekend's showpiece match when they raced into a 3-0 lead within the opening 23 minutes.

First Dimitrios Petratos scored from the penalty spot, before the home side's Andreu Guerao turned the ball into his own net.

Then, after leading goalscorer Jamie Maclaren added a third goal, the outcome looked inevitable.

However, that advantage was cut to just one goal by the break as Wanderers responded through Romeo Castelen and Brendon Santalab.

Dutch midfielder Castelen then took centre stage after the restart as he completed his hat-trick to put his side 4-3 in front with goals in the 53rd and 59th minutes, the latter of which was a half-volley from the edge of the box.

However, in keeping with the drama, there were nine minutes remaining when Brisbane's Maclaren stole in at the back post to force extra time.

Both sides had chances during the added 30 minutes to nab the all-important ninth goal of the game, which eventually went the way of the Wanderers in the 102nd minute.

Mark Bridge sent the ball across the face of goal and substitute Dario Vidosic was on hand to fire into the roof of the net.

His team will now battle it out with Adelaide United to lift the trophy.