A 10-man Macarthur FC have defied the odds to claim a 2-0 upset win over Central Coast in the opening A-League elimination final.

In their first season, Macarthur silenced a passionate home crowd at Central Coast Stadium on Saturday night with two extra-time goals to book a semi-final showdown with this season's premiers Melbourne City next weekend.

The Mariners were in the box seat to celebrate their finals return after a seven-year exile when the Bulls' James Meredith was sent off in the 75th minute for bringing down Marco Urena.

The Mariners' danger man clearly handballed before the Meredith challenge but the VAR judged it accidental and the red card stood, much to the disbelief of visiting coach Ante Milicic who was left shaking his head after watching the big-screen replays.

Still 0-0 at the end of regulation time, the finals dream became a nightmare for the Mariners when Charles M'Mombwa found the back of the net three minutes into extra-time.

After an Ivan Franjic cross, Markel Susaeta hit the far post and M'Mombwa's header off the ricochet set up the Bulls' first-ever win over the Mariners at the fourth attempt.

Teenager Michael Ruhs put the icing on the cake when he was set up by Jake Hollman in the 121st minute.

"The send-off changed things for us but in the end ... I am delighted with the performance. The boys really showed what they are about tonight," Bulls coach Milicic said.

Macarthur finished the game without key stars Matt Derbyshire (hamstring) and Susaeta (leg) but hung on to extend the career of former Socceroos captain Mark Milligan who will retire at season's end.

"This was a massive game for our football club in our inaugural year but I always felt we had it in us," Milicic said of the Bulls, who finished sixth to scrape into the finals.

"We are alive for another week (but) we deserve to be where we are."

Milicic refused to bite when asked about the sending-off and another incident in which the Mariners' Jack Clisby appeared lucky to avoid a red card for a dangerous tackle on Ruhs in extra-time.

"I just want to concentrate on the performance, not speak about any dubious decisions that went against us. I am looking ahead," he said.

Despite being without their inspirational captain Oliver Bozanic (calf), Central Coast were the overwhelming favourites after finishing third.

However the fairytale abruptly ended for the 2013 champions who were appearing in their first finals campaign since 2014 after reversing a run of four wooden spoons in five seasons.

"It is a gut-wrenching feeling but our execution let us down a little bit," Mariners coach Alen Stajcic said.

"I am obviously very proud of our season but just not happy about tonight."