The 21-year-old sealed victory for his Duckhams Yuasa Racing with Redline team in the 350th Porsche Carrera Cup GB race.
It was a dream start for Ginetta champion Adam, who has switched to Porsche after winning the coveted title of Porsche Junior GB Driver for this year and next.
The intensity of the competition was clear from qualifying at the iconic Donington circuit in Leicestershire, where the first 14 drivers were separated by less than one second.
Having missed out on the front row by just 0.059secs, Adam started third in the opening event of this 20th Carrera Cup season but soon moved into second before forcing the leader into a mistake through the chicane and passing superbly for victory.
In the reverse-grid race which followed, broadcast live on ITV4, Adam started fourth and just missed a podium place by 1.5secs.
Those results leave Smalley joint-first on the leaderboard going into the second round of the championship at Brands Hatch on May 14 and 15.
Back home in Poulton between races, Adam told The Gazette: “We didn't expect to win but it was a dream start.
“It's a brand new car and it was an intense pre-season getting my head around the differences after driving Ginetta cars previously.
“But I was confident in our ability after qualifying and managed to piece everything together in the first race.
"I had a good start and knew I had the pace to catch the leader.
"I'd like to thank everyone at Duckhams Yuasa Racing with Redline for a perfect start.
"I’m really looking forward to Brands Hatch and I’ll be doing everything I can to stay at the top.”