George Gregan claims Ireland should take inspiration from golfer Cam Smith in their bid to break through that Rugby World Cup quarter-final barrier for the first time.
Gregan was present at St Andrew's in July to witness Smith, a fellow Aussie, claw back a three-shot deficit with nine holes left to wreck McIlroy's dream of winning the British Open for a second time.
World Cup winner Gregan believes that Smith's career-best display in that final round is the kind of performance Ireland need if, as expected, they meet either the hosts or the All Blacks in the last eight at France 2023.
READ MORE: Peter O'Mahony: Ireland hungry to stay ahead of the curve by beating Australia
"I'm not being smart but they'll just win a quarter-final and then they're two wins away from being world champions," said Gregan.
"I watched Cam Smith win his major, he knew he had to birdie five holes in a row and get it done.
"The opportunity is there - you either do it or you don't. And when they do break through it, Ireland will be very hard to beat.
"You either win and you go forward or you go home, so it starts getting serious then. Break through that wall and they'll be very hard to beat because they are playing very good rugby."
Gregan loved Smith's against-the-odds achievement in reeling in McIlroy. "It was what live sport is all about," said the 139-times capped Wallaby.
"In live sport, someone - or some team - will do something they've never done before because of the occasion.
"Cam had to come up with a PB. Rory wasn't going to give it to him."
Smith had never won a major before and was in the kind of underdog role Ireland will find themselves in if they make it back to the World Cup quarter-finals, hoping to go further than any previous Ireland team.
"It's about executing in that moment," Smart Ball ambassador Gregan said.
Ahead of tonight's Ireland versus Australia clash, Gregan notes the parallels for the hosts in how they were going in 2018 - a year in which they beat the Wallabies in a summer series - and how they are performing now as the world's top ranked side.
"I remember 2018, what a year," he said. "And then a few injuries, a couple of results...it's sport and confidence is a real funny thing.
"There's no way you would have predicted what happened in 2019 a year out - and that's why it's difficult to be talking about a World Cup now, there's still so much water under the bridge to come before then.
"It's about the mindset of your players going into it, thinking, 'OK, it's a new tournament'.
"That's the really hard thing about a World Cup - when you finally get there it's a seven week sprint and what you've done before that, to be fair, really doesn't matter.
"It can help you because you can call upon those big moments - but it's still a different beast.
"It's good to be winning and playing well going into it. But it's always dangerous to be talking about a World Cup this far out because there are so many variables still to play out."
Sage is the Official Insights Partner of Six Nations Rugby and will be powering the Smart Ball this Autumn Nations Series. #SageInsights
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