GP2 veteran Marcus Ericsson topped the first day of the category's final post-season test at Jerez on Thursday.
The Swede, driving for DAMS, pinched top spot from Carlin's Felipe Nasr in the afternoon.
Nasr's morning time was good enough to keep him in second for the remainder of the day, with former GP3 racer Alexander Sims third for Addax.
Stephane Richelmi and Stefano Coletti were next up for Trident and Rapax respectively, with Italian F3 race winner Kevin Giovesi sixth fastest for Lazarus.
The test had got off to a slow start in the morning, with poor visibility due to fog at Turns 6 and 7 leading to a red flag.
Many drivers opted to sit out the early running when the track was declared fit for purpose, leading to a flurry of activity just before lunch as Nasr set the pace.
A change in conditions at the end of the day as temperatures dropped led to a similar surge of activity at the top of the timesheets in the afternoon session.