Adelaide, the A-League's bottom-club scored goals at the beginning of both halves to claim the contest which mathematically ends any hope of Brisbane making the top six.

Postecoglou said after the loss: "Tonight was the biggest game of the season and we probably played our worst game of the season."

The former South Melbourne coach now has a record of 5 wins, 3 draws and 7 losses since taking over at Suncorp in mid-October.

He added: "I think I need, and we need, to have a good look in the mirror and admit that performance just wasn't good enough.

"Once we've done that we have to get back out on the track and work hard to make our next game a better performance."

Brisbane travel to Perth Glory for a difficult away trip next Saturday in the final round of the regular season.