Peter O'Mahony believes clinching a long-awaited series win in Australia in Sydney on Saturday will be "right up there" with Ireland's Grand Slam triumph.

Ireland levelled the series in Melbourne last weekend with their first victory in Australia since 1979.

That was the same year they last won an away series against the Wallabies, so captain O'Mahony knows Joe Schmidt's side are on the brink of something special ahead of the final Test at the Allianz Stadium in Sydney before it is knocked down next year and rebuilt.

"It would be up there. None of this group has done it. The last time we won a Test here was 1979, so that says enough of how hard it is to win over here." said O'Mahony, who will switch to openside flanker for the decider.

"To talk about winning a series over here is up there with one of the biggest challenges in world rugby.

"We want to go and win [on Saturday] but we know we've got to get our process right and our performance is paramount.

"If we don't put in a good performance, we could be well beaten by 30 or 40 points if we're not on the ball."

O'Mahony cannot recall the last time he played at openside, but said he has no problem with a change of role as he prepares to earn his 50th cap.

"I don't know, actually,” he said when asked about the last time he played at number seven.

"CJ [Stander] would be well able to play seven as well. It changes a couple of small little roles but it’s something I was comfortable with from earlier on in the week when they asked me to slot in.

"Any opportunity you get to start in an Irish jersey – I'd take playing in the front row because it's a special honour."