Sergey Sirotkin topped the additional Formula Renault 3.5 test session at Monza on Thursday afternoon ahead of this weekend's season opener.
The Russian driver moved to the top of the times just as rain started to fall at the far end of the circuit, affecting the Lesmo corners in particular. The ISR driver's lap edged him ahead of Arthur Pic, who had gone fastest for new team AV Formula just before that.
Will Stevens had enjoyed a spell at the top of the times before Sirotkin and Pic got their laps in as the first drops of rain fell, and the Briton ended the day third fastest for P1 Motorsport.
Stevens ended up a few tenths of a second shy of the top two, but he was at the head of a very closely bunched group, just edging out pre-season favorite Antonio Felix da Costa and reigning Formula Renault Eurocup champion Stoffel Vandoorne.
Thursday's session was the first of two additional tests being given to teams this season as a result of the cancelled day of running at Aragon in February due to snow. The teams will get another three-hour session on the eve of the second round of the series at the track where the original test took place.