The Michelin-equipped ERC points leader took 20min 54.8sec to complete the 34.57-kilometre Torre di Cicerone test with a 2.3sec margin over Pirelli-shod Andrea Crugnola, who is chasing his third consecutive victory on the all-asphalt event.
But it could have been a different story had the Pole failed save a moment when he went wide on a right-hander and briefly went off the road.
Marczyk had earlier set the joint fastest time with Giandomenico Basso through SS2, Collepardo Pozzo d’Antullo to move ahead of overnight leader Boštjan Avbelj, who was quickest on the Rome super special stage on Friday evening.
Behind second-placed Crugnola, double ERC champion Giandomenico Basso is third, 3.7sec adrift of Marczyk, with Andrea Mabellini slipping to fourth, 4.3sec off the lead.
Mads Østberg is fifth followed by Simone Campedelli and 2022 European chakmpion Efrén Llarena, who is back on ERC duty after missing the three gravel rounds.
Colosseum super special stage winner Boštjan Avbelj, Fabio Andolfi and Roberto Daprà complete the current top 10 ahead of the 13.05-kilometre Santopadre stage, SS4, from 11:10 local time.