The three-time series champion stepped away from the DTM after securing the 2020 title in the final Class One season before the championship's switch to GT3 rules for 2021, but returned this year following Audi's withdrawal from Formula E.
After a difficult opening round in Portimao where he scored no points, Rast got back onto the podium last time out at the Lausitzring then converted his first pole of the season in the opening race at Imola on Saturday to a comfortable victory over old rival Nico Muller.
When reflecting on what he called "a perfect race", Rast revealed that his success had been "a bit unexpected" as "before the season I didn’t really expect to fight for wins or for podiums".
Asked by Autosport to clarify his comments, Rast explained: "I had to adapt to the car again, it took me a bit longer than I was hoping obviously.
"I didn’t really expect to fight for wins because a GT3 car is so special, it’s made for specialists I always say.
"Those drivers drive these cars for seven, eight years, they have so much experience and I didn’t really expect to fight them.
"Now I got proven wrong, but I also have to say we put a lot of effort and work into the set-up of the car which is now suiting my driving style a lot better.
"It’s a big team effort that I’m standing now here and fighting for winning races."
While admitting that the team has "found a good baseline" that he anticipates running to the end of the season, Rast stressed that he doesn't expect the DTM to revert to the private head-to-head battles between he and Muller that characterised the final years of the Class One era.
Rast's 25th career victory puts him on 49 points, fourth in the championship and 21 adrift of standings leader Sheldon van der Linde.
"I think it’s still a lot different to 2020," the 35-year-old said.
"In 2020 we had Audi dominating the whole DTM season and it was only Nico, me and Robin [Frijns] fighting for wins basically.
"Now it’s a lot different, we have so many drivers fighting for wins, each track suits a different track better, so obviously we cannot expect to win every race weekend or fight for podiums.
"We will also have races where we are happy with two or three points only."
Rast added that his win "wasn’t as easy as it might look" as he "had a few moments, especially when Nico was behind me in the beginning of the race, where I almost lost the car".
But he did have enough of a margin to enjoy the benefits of air conditioning in the sweltering afternoon temperatures.
"I was playing around with the air-con and looking if Nico was catching up," he said.
"Once he got a bit closer I switched it off again."
