Lorenzo Zanetti set the WSS pace during opening practice for the Italian round at Imola.
The Italian, just eighth in the present standings, rode his Pata Honda to a best time of 1m 52.284s, allow him to fend off Intermoto Kawasaki's title leader Florian Marino by 0.177s.
While Zanetti led much of the session, team-mate Michael VD Mark - fresh from his first WSS win, in front of his home fans, at Assen - joined Marino is making late progress to seal third place on the timesheets.
That can at the expense of multiple champion Kenan Sofuoglu, who spent much of the session second to Zanetti - and briefly led at the midway stage - on his way to fourth (+0.400s).
On form DMC Panavto-Yamaha rider Kev Coghlan completed a top five covered by less than half-a-second, with a sizeable 0.4s gap to Riccardo Russo.
Frenchman Marino starts round four with a slender four-point title advantage over VD Mark.