It is Australia’s first time in the knockout stage since 2006, which was the only other time that they advanced out of the group stage.
The Socceroos contained Denmark at Al Janoub Stadium before stinging them on a counterattack in the 60th minute when Leckie burst into Denmark’s end, wrong-footed defender Joakim Maehle and fired low past goalkeeper Kasper Schmeichel.
Denmark’s coach Kasper Hjulmand brought on all the attacking firepower he could muster as he desperately sought the goals that have eluded his side in Qatar.
But Australia held on to claim second place in Group D behind France. A second-half goal helped Tunisia beat France – but Australia’s win over Denmark sealed their exit.