Gilmour (left) and Wellens both scored for Great Britain
Australia: (6) 12
Tries: Inglis, Lockyer.
Goals: Lockyer (2)
Great Britain: (6) 23
Tries: Wellens, Peacock, Gilmour, Raynor.
Goals: Long (3)
Great Britain resisted some early brutality from Willie Mason to win an enthralling Test match and open their Tri-Nations account.
Greg Inglis put Australia ahead after a Ben Hornby interception before Paul Wellens made it 6-6 at the break after a superb dummy from Sean Long.
Jamie Peacock then crashed over before Darren Lockyer converted his own try.
But tries from Lee Gilmour and Gareth Raynor, plus a drop-goal from Long, sealed a famous win.
It was a highly physical, tough game of rugby league that GB, pilloried all week in the Australian press, fully deserved to win - in the process inflicting the first defeat for Ricky Stuart as Kangaroos coach.
Great Britain, after their first win in Australia since a a 33-10 victory in Melbourne 14 years ago, now have two points from their first two Tri-Nations games and are in a good position to make the final.
Long, criticised so often in the past for his performances in a Great Britain shirt, was superb, as was skipper Peacock, who led from the front.
I think they might start taking us seriously now
The first points of the game were not put on the board until the 29th minute, when Hornby's interception led to winger Inglis racing the length of the field.
Up until that point GB had dominated a brutal opening phase of the match that saw Australian forward Mason floor Stuart Fielden with an early punch.
Mason escaped with a telling-off from referee Ashley Klein and then, with 10 minutes gone, led with the elbow in a very late challenge on Long after the GB half-back had kicked the ball.
Again Mason, who had now been guilty of two incidents of serious foul play, remained on the field.
Yet, as with last week's Test match in New Zealand, GB bossed the early phase of the game in terms of field possession and territory without scoring any points.
At crucial moments an errant pass or an unnecessary offload released the pressure on the Australians.
And they were made to pay when a gamble from Hornby paid off in spectacular style.
Mason (left) was involved in some brutal incidents
He charged from the Kangaroos defensive line and intercepted Long's pass before slipping the ball to Inglis, who crossed under the sticks for a try that Lockyer converted.
But GB were not to be denied and a superb dummy from Long deceived Lockyer and the St Helens half-back broke through the line before passing to Wellens for his club-mate to score.
Long added the extras and GB, who had lost Brian Carney to a hamstring injury, resisted some strong Kangaroos pressure to go in level at the break.
Britain started superbly after the restart, working their way up the field before Peacock bundled his way over from short range despite numerous Australians trying to prevent him from touching down.
The try was awarded on the benefit of the doubt rule and Long added the extras as Aussie Stadium fell silent.
But Australia soon underlined their attacking threat, bursting through the GB line before Lockyer's angled kick went into touch with Jamie Lyon lurking.
Wellens scored a crucial first-half try for Great Britain
And poor positioning by Leon Pryce allowed Inglis to break forward before slipping an inside pass to Lockyer, who raced clear to score before adding the conversion.
A kick through from Lockyer, combined with a slip by Wellens, seemed to set Hornby up for a certain try but he collided with Raynor as he went to touch down and dropped the ball while sustaining a heavy blow that left him dazed and confused.
And having survived that scare, GB won a repeat set and made the most of the opportunity, with Gilmour bursting through a double tackle to score under the posts, again Long adding the extras.
Suddenly it was Australia guilty of handling errors at key times - Mason for example dropping the ball with the line in sight.
Long missed a straightforward penalty and with a drop-goal attempt as he looked to extend GB's lead.
But his misses were not to be punished when GB showed amazing composure after Long broke through and passed the ball to James Roby with four minutes left.
From the next tackle the Lions swept the ball left for Raynor to cross in the corner and although Long's conversion attempt hit the posts, he scored a drop-goal minutes later to seal a famous victory.
Great Britain: Paul Wellens, Brian Carney, Keith Senior, Kirk Yeaman, Gareth Raynor, Leon Pryce, Sean Long, Stuart Fielden, Terry Newton, Jamie Peacock (captain), Gareth Ellis, Gareth Hock, Sean O'Loughlin.
Interchange: James Roby, Adrian Morley, Lee Gilmour, Jon Wilkin.
Australia: Karmichael Hunt, Brent Tate, Mark Gasnier, Jamie Lyon, Greg Inglis, Darren Lockyer (captain), Ben Hornby, Mark O'Meley, Shaun Berrigan, Petero Civoniceva, Willie Mason, Nathan Hindmarsh, Luke O'Donnell.
Interchange: Cameron Smith, Anthony Tupou, Brent Kite, Antonio Kaufusi.