Germany's Nico Rosberg stayed ahead of team mate Michael Schumacher to put Mercedes on top of the timesheets in practice for the season-opening Bahrain Grand Prix on Friday.
After compatriot Adrian Sutil had stolen some of the returning seven-times champion's limelight in the first session with the quickest time for Mercedes-powered Force India, Rosberg went faster in the afternoon.
The son of former champion Keke lapped the newly extended Sakhir circuit in one minute, 55.409 seconds, nearly half a second quicker than his 41-year-old team mate in third place.
McLaren's Lewis Hamilton was second, running faster than team mate and reigning champion Jenson Button who had been ahead in the morning.
Mercedes engined cars filled the top four slots.
Spain's double world champion Fernando Alonso limbered up for his Ferrari race debut with the second best time in the first session and then ninth after lunch.
While practice times can be misleading, with drivers trying out different set-ups and running with varying fuel loads, all eyes were on Schumacher's pace after an absence of three seasons.
With Mercedes returning as a works team for the first time since 1955 after taking over champions Brawn, the former Ferrari great was 10th in the morning and more than 0.4 seconds slower than Rosberg.
ILLUSTRIOUS MARQUE
Lotus, an illustrious name returning after a 16-year absence were the best of the three all-new entrants although they were an age off the pace.
Finland's Heikki Kovalainen lapped 18th fastest, 5.464 seconds slower than Rosberg, with Italian Jarno Trulli 19th.
Virgin Racing's Timo Glock was 6.6 seconds slower than the fastest car while Brazilian Bruno Senna was 11.5 seconds away from Rosberg's time.
With the HRT (Hispania) team unable to test the car before arriving in Bahrain, the return of the Senna name to a grand prix weekend for the first time since the death of Ayrton at Imola in 1994 was limited to what amounted to a shakedown.
Indian rookie team mate Karun Chandhok did not even manage to get out on track, forced to sit out both sessions while mechanics worked on his car.
"We have had a lot of problems, we can't seem to get the clutch and gearbox working," he said.
"It's such a shame for the mechanics, they have worked all night without any sleep -- so I feel for them. It's some sort of electronic or hydraulic issue, it's not mechanical...it's a very difficult first day in F1 for me."
