The nuggety midfielder had another big day on Sunday as he was again at the heart of Hearts' 2-1 statement home win over Rangers at Tynecastle that's put them six points clear of champions Celtic atop the Scottish Premiership at Christmas.
The last club to win Scotland's top-flight league title – other than the Glasgow 'Old Firm' of Celtic or Rangers – was Alex Ferguson's Aberdeen in 1985, but Hearts are showing no signs of relenting as they threaten to end the 40-year duopoly.
Danny Rohl's Rangers had been buoyed by an 11-game unbeaten run in the league, but first-half goals from Hearts' duo Stuart Findlay and captain Lawrence Shankland, countered only by Youssef Chermiti's stoppage-time consolation, may have scuppered their title chances already as they're now 12 points adrift.
Hearts have won all four of their matches against Celtic and Rangers this season and are the first beyond the big two to top the table on Christmas Day since 1993.
And one of their key drivers in a season when they've only lost one league game is the diminutive but big-hearted Sydneysider Devlin, who's been a firm favourite at the Edinburgh club for five seasons.
Before Sunday's match, TV pundit Chris Sutton, the former Blackburn, Celtic and England striker, described him on Sky Sports as "the heartbeat of the Hearts team", and the 27-year-old again demonstrated that with another energetic and tigerish midfield display.
Last month, he captained the team for the first time in the absence of Shankland, and revealed in a pre-match interview with Sky: "I feel like I'm playing well, really enjoying it and getting the armband when a couple of leaders go off is really special.
"I feel we're getting back to where Hearts should be."
Back in Socceroos coach Tony Popovic's thoughts, having been recalled to the squad for the North American tour, Devlin is also determined to be involved in Australia's World Cup bid back there next year.
"That's everything now. I don't shy away from the fact of how important it is for me to play for my country, and how much it means to me and my family because it's the pinnacle," he said.
In 2022, Devlin was in the World Cup squad but was an unused sub. He did, however, end up with the ultimate souvenir -- Lionel Messi's shirt after the great Argentine's 1000th professional match in the last-16 tie victory over the Socceroos.
"My plan this time, is to hopefully get there and get on the pitch. That's the most important thing," he said.
After Hearts beat Rangers, struggling Celtic, fresh from losing last week's League Cup final to St Mirren, earned their first win under new boss Wilfried Nancy, earning a 3-1 victory over 10-man Aberdeen at Parkhead to stay six points behind with a game in hand.
