Marcus Ericsson and Dani Clos proved quickest on the third day of testing at Jerez in Spain, taking one session apiece - although it was the former that surprised by setting the best time overall.
After two sunny days in Jerez, the last day started wet as rain continuously fell onto the Spanish track for most of the three-hour morning session.
Five new drivers joined the field today - namely 2008 GP2 runner-up Bruno Senna returning to iSport, Chris van der Drift driving for Piquet GP, Edoardo Mortara at Telmex Arden, newcomer Jon Lancaster joining DAMS and five-time World Rally champion Sébastien Loeb at DPR.
In difficult track conditions, the opening session was briefly interrupted twice - first by Fabio Onidi at Trident following mechanical gremlins, and then after Marco Bonanomi and van der Drift simultaneously spun and stopped at two different parts of the circuit.
In a drying session, the drivers' lap-times improved notably towards the latter stages and it was both Fat Burner Racing Engineering racers, Clos leading Jérôme d'Ambrosio, who claimed the top spots ahead of Luiz Razia driving with Barwa Addax.
Will Bratt finished the morning first rookie although newcomer Alexander Rossi at DAMS was fastest in wet conditions until fifteen minutes before the chequered flag when a hydraulic pump problem ruined the American's efforts.
In the afternoon the sun made an appearance and although the track conditions seemed less tricky, the session was still interspersed by six red flags - including one following a shunt from Mortara, who lost control of his car at Turn 9 and who ended his day prematurely as a result.
The surprise of the day however, came from newcomer Ericsson who, at the wheel of the ART car, led the way on a 1m 25.970s lap.
Clos, d'Ambrosio and Razia meanwhile confirmed their good form again in the top five while another impressive newcomer, Swiss Fabio Leimer at Ocean Racing, found his way to third place.
GP2 Series testing will now resume next month at Le Castellet, running from November 10-12.
In the meantime though, the GP2 teams - minus Racing Engineering - will fly to Abu Dhabi where they will be joined by Meritus for the opening of the third GP2 Asia Series season. A pre-season test session will take place on October 23-24 at the Yas Marina Circuit.