The nine-time motorcycle racing world champion was behind the wheel of a Team WRT Audi R8 for two sprint races, finishing 13th then eighth, on Sunday at Brands Hatch in the UK.
Rossi, now 43, was forced to use all of his experience on the very first lap when he steered beyond a collision that ended the race for two of his Team WRT teammates, Jean-Baptiste Simmenaur and Benjamin Goethe.
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Rossi gave way to Belgium’s Frédéric Vervisch midway through the sprint - they finished in P13 with a time of +33.760.
Rossi then impressively finished the second race of the day in P8 with a time of +40.216.
Ulysse De Pauw and Pierre Alexandre Jean won the first race in AF Corse’s Ferrari 488 GT3.
The second was won by Timur Boguslavskiy and Raffaele Marciello in an Akkodis ASP Team Mercedes-AMG GT3.
Rossi’s first race on four wheels last month since exiting MotoGP was marred by a pit stop mishap where he accidentally drove past his own crew.
His next outing will be 13-15 May at Magny-Cours in France.
Why Rossi races on after retiring from MotoGP
“I always had an idea to race with cars, since when I started with motorcycles," he said on Friday.
“This idea with GT3 helped me to stop with the bikes!
“To stop was very difficult. I drove cars in the past just to improve my skills.
“I want to be competitive.
“You need something - you need to feel the adrenaline, to remain a driver, to remain on the track, to jump in the car, to wear the helmet.
Rossi warned his new rivals: “The good drivers have a big difference compared to me.
“My lap times were not so bad. But I need to arrive at that performance earlier. I need to improve my skills. I am not far from the top guys but they are faster than me."
The verdict on Rossi from his teammate
Vervisch said about Rossi’s apprenticeship in a new sport: “The best I’ve had so far. I am experienced with driver coaching.
“What he has done is impressive. He is being modest. You tell him something once, and he does it.
“For him - he tries, it doesn’t work, he says ‘OK, try again’.
“He can do the same as us, or even better. He is just yet to bring it all together.”
Lewis Hamilton: MotoGP 'more hardcore' than F1!
Rossi was told that racing on two wheels is "more hardcore" than four wheels by seven-time F1 champion Lewis Hamilton last month.
“I think MotoGP is more hardcore,” Hamilton admitted. “These guys don’t have seatbelts.
“When they have a crash, it is big. It is hard for them to improve safety.
“The fear factor for them is always there, and has been there for years.
“Our sport is getting safer and safer.
“We watch [MotoGP] in complete shock. It is nerve-wracking.”
Rossi told Hamilton about racing in GT World Challenge Europe: “I am excited for a new adventure, racing with a car. It is the second chapter of my career.”
Hamilton asked: “When are you coming to Formula 1?”
Rossi: “Unfortunately I am too old!
“To drive a car or to ride a motorcycle? It is different but also the same. The lines are similar, and the braking. You have to be fast.
“If you can drive a car, you can also ride a bike, and the opposite.”