Valtteri Bottas went quickest for his Williams team on the second day of the second and final pre-season test at Barcelona on Wednesday.
Bottas appeared to be working on qualifying runs and ended up with the best time after putting on the supersoft tyres later in the day.
His best time of 1:23.261 relegated Mercedes driver Lewis Hamilton to second, the Briton having set the pace in the morning with soft tyres.
Teammate Nico Rosberg replaced Hamilton in the afternoon and, like the Briton did yesterday, carried out a trouble-free race simulation.
Rosberg finished down in ninth place as Mercedes had another prolific day (164 laps).
Kevin Magnussen kept Renault near the top of the times, going third-quickest after 126 laps. His best time was set on softs.
Ferrari enjoyed its most productive day of testing so far as Sebastian Vettel completed 151 laps on his way to the fourth quickest time of the day. The German was the quickest driver on medium tyres.
Carlos Sainz (Toro Rosso), Force India's Sergio Perez and Pascal Wehrlein in Manor rounded out the top 10, the German in 10th behind Rosberg.
Marcus Ericsson got his first taste of the new Sauber C35 after taking over from teammate Felipe Nasr, but the Swede did not have a very productive session.
After spending a lot of time in the pits, Ericsson took to the track just before lunch and then his day hit more trouble when he spun into the gravel at Turn 4 one hour from the end.
The Sauber took to the track again with two minutes to go.
The Haas team, meanwhile, endured a disastrous day, its poor second week of testing continuing.
Esteban Gutierrez, who had only managed 23 laps yesterday due to a problem with the fuel system, failed to set a time after completing only an installation lap before he suffered turbo problems that kept him in the garage all day.
Teammate Romain Grosjean is scheduled to replace the Mexican tomorrow.
Day 2, final testing times:
|6||D. Ricciardo||Red Bull||1:25.235||135|
|7||C. Sainz||Toro Rosso||1:25.300||166|
|8||S. Perez||Force India||1:25.593||128|
|12||E. Gutierrez||Haas||no time||1|