Kevin Ceccon set the pace for MW Arden on the opening day of GP3's postseason test at Jerez.
The 19-year-old Italian, who finished ninth in this year's championship while driving for Ocean, lapped the Spanish track in 1m35.451s to end the day more than half a second clear of the field.
Afternoon rain prevented anyone from mustering a late response, meaning Robert Visoiu's 1m35.903s remained good enough for second.
Tio Ellinas, fastest in the wet, ended the day in third ahead of David Fumanelli, Melville McKee and Alex Fontana.
McKee was the quickest newcomer in the 20-car field, which featured six drivers from the regular season.
British F3 champion Jack Harvey, making his series debut with Carlin, was 14th fastest in the morning and second fastest, less than half a second down on Ellinas, in the afternoon.