Lewis Hamilton set the fastest time of the opening practice session for this weekend's Spanish Grand Prix at Barcelona.
McLaren set the top two times, with Hamilton finishing the 90-minute session half a second clear of team-mate Jenson Button.
Red Bull was the first team to get up to speed and for a while it looked as though Mark Webber and Sebastian Vettel would lead the way. But first Michael Schumacher and Button, and then Hamilton, beat the 1m22.0s of the Red Bulls.
Button and Schumacher set their best efforts, 1m21.6s and 1m21.7s just a couple of minutes before Hamilton lapped in 1m21.1.
There were no improvements at the sharp end in the last half hour as team's switched to work on high fuel loads.
Nico Rosberg completed the top six in the second Mercedes, with the Renaults of Robert Kubica and Vitaly Petrov sandwiching Fernando Alonso's Ferrari from seventh to ninth, while Kamui Kobayashi's Sauber rounded out the top 10.
Paul di Resta set the 13th quickest time in his regular slot as Force India test driver, this week in place of Adrian Sutil for the first session - two places ahead of Vitantonio Liuzzi.
Christian Klien took to the track for the first time this season, taking Karun Chandhok's place for the opening practice session, and finished 22nd - half a second faster than HRT team-mate Bruno Senna.
Heikki Kovalainen was fastest of the new team runners in 18th place, nearly a second ahead of Lotus team-mate Jarno Trulli and under two seconds adrift of the established runners. Kovalainen had to have his throttle replaced during the session after a problem with the throttle sensor hindered his early runs.
Timo Glock got his hands on an evolved version of the Virgin for the first time and finished the session 20th, while team-mate Lucas di Grassi was three tenths further back, 21st, in the old car.
Williams was another team to bring just one new car to Barcelona. Rubens Barrichello was 16th quickest despite a problem with the oil system on the new version, a tenth faster than team-mate Nico Hulkenberg who stopped out on track 10 minutes from the end with what looked like an engine failure on the old car.
Pedro de la Rosa completed just three installation laps before his Sauber was sidelined for the remainder of the session with a gearbox problem.
Pos Driver Team Time Laps
1. Hamilton McLaren-Mercedes 1:21.134 21
2. Button McLaren-Mercedes 1:21.672 + 0.538 14
3. Schumacher Mercedes 1:21.716 + 0.582 12
4. Webber Red Bull-Renault 1:22.011 + 0.877 27
5. Vettel Red Bull-Renault 1:22.026 + 0.892 22
6. Rosberg Mercedes 1:22.070 + 0.936 19
7. Kubica Renault 1:22.202 + 1.068 22
8. Alonso Ferrari 1:22.258 + 1.124 19
9. Petrov Renault 1:22.397 + 1.263 23
10. Kobayashi Sauber-Ferrari 1:22.492 + 1.358 26
11. Buemi Toro Rosso-Ferrari 1:22.588 + 1.454 24
12. Massa Ferrari 1:22.975 + 1.841 22
13. di Resta Force India-Mercedes 1:23.030 + 1.896 21
14. Alguersuari Toro Rosso-Ferrari 1:23.110 + 1.976 31
15. Liuzzi Force India-Mercedes 1:23.284 + 2.150 19
16. Barrichello Williams-Cosworth 1:23.312 + 2.178 22
17. Hulkenberg Williams-Cosworth 1:23.471 + 2.337 20
18. Kovalainen Lotus-Cosworth 1:25.329 + 4.195 17
19. Trulli Lotus-Cosworth 1:26.244 + 5.110 20
20. Glock Virgin-Cosworth 1:26.340 + 5.206 23
21. di Grassi Virgin-Cosworth 1:26.694 + 5.560 24
22. Klien HRT-Cosworth 1:27.250 + 6.116 26
23. Senna HRT-Cosworth 1:27.752 + 6.618 27
24. de la Rosa Sauber-Ferrari No time 3
All Timing Unofficial