Nico Rosberg kept Mercedes at the top of the timesheets at the midway stage of day three testing at Jerez, with Romain Grosjean and Lotus this time the fastest of the 2012 runners.
Cold conditions produced a slow start to the morning, with only Sergio Perez able to break into the 1m19s early on.
The conditions also caught out Force India's third driver Jules Bianchi, who lost the rear and skipped sideways through the gravel at Sito Pons, leading to the day's first - and so far only - red flag period. Force India is yet to get back underway.
Grosjean moved into the ascendancy at the restart, topping the timesheets with a 1m18.901s before lowering his own benchmark several times. He eventually ended on a 1m18.419s, the fastest lap seen thus far from a 2012 car.
That looked good enough to keep the Frenchman fastest at the half-way point, only for Nico Rosberg to go fastest in all three sectors - producing a 1m17.613s to go clear at the top.
As was the case yesterday with Michael Schumacher however, Rosberg's time came in the 2011-spec Mercedes, being used to evaluate Pirelli's new rubber before the team debuts its 2012 challenger at the first Barcelona test.
Lewis Hamilton, taking control of the McLaren MP4-27 for the first time, finished third fastest but found himself more than a second down on Grosjean.
Jean-Eric Vergne, also getting his first taste of the Toro Rosso, was less than three tenths back in fourth, with Perez's early benchmark good enough to keep him fifth.
Reigning world champion Sebastian Vettel managed 28 laps in Red Bull's RB8 but did not match team-mate Mark Webber's pace Wednesday pace. He currently lies sixth overall with a low 1m20s his best effort.
A large crowd had gathered for Fernando Alonso's first day in Ferrari's F2012, but they saw precious little of the Spaniard in the first two hours as Ferrari battled with hydraulic issues.
When he was able to get out he got down to a mid 1m20s, putting him seventh.
Bruno Senna and Giedo van der Garde joined today's list of new drivers, slotting in at Williams and Caterham respectively.
Senna ended eighth, more than three seconds off Rosberg, with van Der Garde - Caterham's third driver - a further two seconds back.
Bianchi rounded out the top ten, although he did not register a time due to his early crash. He is due to be replaced by Nico Hulkenberg for the afternoon.
Morning times Pos Driver Team Time Laps 1. Rosberg Mercedes 1m17.613s 74 2. Grosjean Lotus 1m18.419s +0.806 53 3. Hamilton McLaren 1m19.464s +1.851 38 4. Vergne Toro Rosso 1m19.734s +2.121 41 5. Perez Sauber 1m19.770s +2.157 31 6. Vettel Red Bull 1m20.154s +2.541 28 7. Alonso Ferrari 1m20.412s +2.799 29 8. Senna Williams 1m21.293s +3.680 61 9. Van der Garde Caterham 1m23.505s +5.892 40