While they were far from their ruthless best the Roar still deserved the victory in front of 10,166 fans at Bluetongue Stadium in the first leg of their major semi-final.

The last time the teams met the Mariners dominated for long periods in a 3-3 draw, but it was a different story this time around with second-half goals from Kosta Barbarouses and captain Matt McKay giving the Roar one foot in the Grand Final.

"I knew at stages we'd have to battle, that's finals football," Postecoglou said. "We did what we had to and scored two quality goals. We worked hard to keep the opposition out.

"It's half-time, that's the way we're treating it. We're in a good position but the job is not done yet."

McKay said the key to the win was holding the Mariners' in-form midfield.

"Tonight was a grinding result but we still played some good football at times," McKay said.

Mariners coach Graham Arnold said the failure to take a host of great chances killed his side.

"It was a game of chances," Arnold said. "We need to be more ruthless. We got the ball to where we needed to but the finishing let us down.

"That's Brisbane, you can't slacken off for a second. 2-0 at home is not a great result; the positive is how we played.

"If we take our chances it's a different game."