Ireland captain Peter O'Mahony reckons a series win in Australia would rank alongside his team's Grand Slam success.
The Six Nations champions' 26-21 victory in Melbourne last weekend set up a winner-takes-all finale against the Wallabies at a sold-out Allianz Stadium in Sydney on Saturday.
Sean Cronin missed training on the eve of the game and, although the Irish Rugby Football Union insists the Leinster man's workload is being managed, Munster hooker Niall Scannell is on standby.
Cronin's inclusion in the team is one of five changes from head coach Joe Schmidt, who has brought in Bundee Aki, Jacob Stockdale, Jack Conan and Jack McGrath, with Leinster fly-half Ross Byrne primed for his international debut off the bench.
It is the final game of a hugely successful season for Schmidt's team and O'Mahony says his players are ready for one last push to end a 39-year wait for a series win over one of the southern hemisphere's big three.
"It has to be right up there," he said of the task at hand.
"None of this group has done it. The last time we won a Test here (before last weekend) was 1979, so that says enough of how hard it is to win over here.
"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.
"There is that fear factor for us that if you're not good, they could put a lot of points on us."
Schmidt said on Thursday that his team would need their best performance of the season to emerge triumphant, and O'Mahony echoed those sentiments.
"We need to build on our performance from last week, and that's the main priority for us," he said.
"There were things we did a lot better last week that are going to have to step up again this week because we know how proud Australia are.
"Their record at home is incredible and a team of their calibre, their performances... we have no doubt it's going to be one of the best they've put in all year.
"We know we have to match that and go beyond if we want to get a win."
Australia coach Michael Cheika made two changes to his side, with Nick Phipps replacing the injured Will Genia and Lukhan Tui coming in for Caleb Timu.
Wallabies captain Michael Hooper is confident his team can close out the series at the second attempt.
"As a stand-alone match, this is really exciting," he said. "That's the unique thing about this June series - it's a three-game shootout, really.
"We can come here and have a deciding game and be a fantastic spectacle. We have talked it up being a Grand Final, so yeah, it's going to be tough on the field.
"But just the buzz around, you look at your phone and people are messaging in, excited about the game, trying to snag a ticket or two. That's great for us as players and I am sure the people will enjoy it."