It was a goal from nothing, the kind of bolt from the blue that bears replaying for years.
The Socceroos levelled in the 60th-minute through a Mark Milligan penalty conversion after Gersbach's strong run into the box was halted by a Cameroon challenge. They had only created a handful of openings and would surely have been finished had Aboubakar been sharper. They gave up two late goals to Eduardo Vargas and Arturo Vidal. If you start thinking in those terms you may miss out on an opportunity along the way.
"I don't think there'd be too many people in football at the moment that'd be backing us", he said. "We are taking it seriously because we know they also need a good result".
Both teams have three points with Chile ahead on goal difference after their 2-0 win over Cameroon and Germany's 3-2 victory against Australia.
Team Cameroon in two games cannot score a goal against the opponent.
Andre-Frank Zambo Anguissa had given Cameroon a deserved lead just before the break, latching on to a long ball over the top and beating Mat Ryan with an outstretched flick.
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The pace and zip that Australia showed in the second period against Germany when Kruse was introduced, however, was largely absent from their play in the first period in St Petersburg. Gersbach, a 20-year-old who plays for Norwegian club Rosenborg, looks a genuine prospect and caused problems beyond winning the penalty, thanks to some unsafe deliveries from the flank.
"I thought Alex was excellent", Postecoglou said. "He's got great technique, great composure and did well for the penalty".
Cameroon certainly didn't lack for spirit either.
While Australia had the better of possession, Cameroon won more of the battles - and the shot count 19 to five.
"In order to play them, we need to be psychologically prepared, at your best, and we are", said the midfielder. And they've always been there for me, giving me advice and guidance - on and off the pitch. Cameroon is not so wealthy in that area.
Chile's Arturo Vidal opened the scoring against Cameroon and he is set to face three Bayern Munich team-mates in Joshua Kimmich, Sebastian Rudy and Niklas Suele. Mabouka's cross was met by Aboubakar who fired over. The Socceroos dominated the ball and held a solid shape, but Cameroon seemed happy for them to play across the back, the Africans also showing in flashes the threat they carried going forward, especially on the counter attack.