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The NASCAR champion had to do it the hard way on the third of three nights after dropping points due to a crash while leading on Night 2.
He was still able to win his heat but the setback contributed to a sixth place start for the big money race.
Local hero Callum Williamson started the A-Main from pole but was quickly bested by James McFadden, fresh off the back of wins on both Prelim nights.
Larson, meanwhile, made early progress to sit fourth before the race was neutralised by a lap 6 shunt that involved Brad Maiolo flipping.
The race only briefly restarted before Ryan Lancaster suffered a similar fate prompting another caution.
On the next restart Larson was able to to jump into second and set after McFadden, the experienced pair engaging in a thrilling duel as the race ran green.
In the end Larson was able to find a way through as they battled traffic, controlling the final few laps to score the landmark $100,000 prize.
Adding to the significance was that it was Larson’s first win on Aussie soil.
McFadden finished second ahead of Williamson, while Brad Sweet was the next-best American in fourth.
Dayne Kingshott recovered from a Night 2 crash to finish fifth ahead of Brock Zearfoss and Jock Goodyer.
Cole Macedo capped off a solid trip to Perth with eighth from Matt Egel and Ryan Newton.
