Francesco Sini topped the one-day International Superstars Series test at Vallelunga on Thursday.
The Solaris Chevrolet driver, who won his first race at Mugello earlier this season, set a best time of 1m42.54s during the rain-affected session, a time that proved unbeatable as the weather deteriorated late in the day.
Meanwhile, new series entrant Durango were on track with two BMW M3s, with Giovanni Berton and Davide Durante both spending time behind the wheel ahead of their respective debuts later this season.
Despite Durante missing out on some early running with fuel pump issues, Berton called the test a success.
"We can say we're really satisfied," he said, after setting a best of 1m44.91s.
"My team-mate and I did not put new tyres on because of the wet weather in the last segment."
Another new addition was the newly-homologated Mercedes C63 AMG Coupe from Roma Racing Team, with Nico Caldarola and Luca Rangoni sharing the running.
"Unfortunately, due to the rain, we could only run two and an half sessions of the four scheduled," said Caldarola.
"[It was] too few to improve the car, that is still needing track time in terms of balancing and weight balancing."