The 17-year-old won his class in both races of the Super3 season-opener with an outright ninth in each, as the third tier of Supercars shared the grid with the Dunlop Super2 Series for the first time, last month.
Robotham was also the class pole-sitter on both days with eighth and then ninth outright in the weekend's two qualifying sessions driving an FG Falcon fielded by MW Motorsport, which won the Super2 title last year and the Super3 title in 2018.
Having only had a small amount of experience driving a Supercars, the former Toyota 86 racer admits he did not forecast such a showing.
“I knew the car would have been quick because obviously Matt White have a good reputation, how they prepare their cars and the speed of them,” Robotham explained to Speedcafe.com.
“So, obviously going in I had a little bit of expectations, but to come away with the win was pretty cool.
“I was just hoping to sort of go in there and be competitive, and learn a new thing every session, but by the time qualifying was through on Saturday morning, it was well above what I expected.
“Hopefully we can sort of do the same thing and replicate it for the rest of the year.”
Robotham's previous running in a Supercar had been limited to two test days in Super2 machinery last year and around 20 laps in the Project Blueprint era Falcon on the Thursday prior to his first race meeting.
He drew similarities to the TA2 car which he had been racing in Asia, although the Supercar was still a challenging proposition initially.
“I did the TA2 racing last year, and they were on a big Hoosier tyre, so the car was very loose and Super3 is a little bit similar,” noted Robotham.
“Supercars are pretty loose cars to drive compared to the 86, though they've got a lot more grunt and I find they've got more grip and braking, more aero, so they're just a lot more fun to drive.
“You have to be sort of precise in what you do and real slow with the throttle applications.
“They're not too bad to get used to but obviously the first couple of laps were pretty scary, getting used to the 600-plus horsepower, whatever it is.”
The Victorian youngster identified tyre management as an area to work on in his next outing.
“(I) Just (want) to improve and work on the car, know what the car's going to do, and just learn how to save the tyres because they were pretty long races, 18 laps at Sydney Motorsport Park,” said Robotham.
“I think in the second race I pushed a bit hard too early and I lost a bit of grip by the end of the race, but hopefully, wherever the next round is, I can sort of replicate; that'd be my ideal situation.
“Mainly learning how to race other guys and what the car's going to do with certain changes, they're sort of my goals going in for the rest of the year.”
Where that next round may be is currently uncertain, given Super2 and Super3 were to have supported the Virgin Australia Supercars Championship's Sandown event in mid-September.