Mark Webber proved the pace of the Red Bull RB5 in first practice for the Brazilian Grand Prix with a sequence of laps late in the 90-minute session that were all fast enough to put the Australian fastest.
Webber, who eventually ended up with a best lap of 1m12.463s, was quick throughout an eventful practice, but in the end was more than 0.4s faster than championship contender Rubens Barrichello in the Brawn.
Sebastian Vettel was third quickest, with Heikki Kovalainen fourth ahead of Lewis Hamilton and Kazuki Nakajima.
Points leader Jenson Button, beginning a weekend that could end up with him being a world champion, appeared to struggle with understeer and ended the session seventh.
The track became busy unusually quickly for an opening practice session as the teams raced against the weather, but it was still the Toro Rossos of Sebastien Buemi and Jaime Alguersuari that were first on to the track and setting the pace.
It wasn't long though before Kimi Raikkonen's Ferrari moved to the top of the times with a 1m14.021s, five hundredths faster than Buemi. It didn't last, as the track rubbered in and Webber quickly moved ahead. This despite the Australian having to use dramatic avoidance tactics to avoid colliding with a dawdling Nakajima.
The Red Bull driver was usurped by Barrichello's Brawn not long after this, but the drizzle that had begun almost at the start of the session, turned into rain around 30 minutes in.
Fernando Alonso's trip across the grass at the hairpin was evidence of the slippery conditions. So the cars headed pit-bound, but not before Vettel set a dramatic 1m12.932s lap to go quickest of all. There then followed a period of calm as the teams and drivers waited out the shower.
McLaren's Kovalainen was the first to try slicks, at the turn of the hour, as the track dried quickly. Moments later the session was red-flagged after Romain Grosjean ran wide at Turn 11 and obliterated a marker board.
The session was re-opened with 22 minutes left, but it still took a while for the drivers to work back down to a decent pace, and with 15 minutes to go, Webber went quickest with a 1m12.805s to make it a Red Bull one-two. But once again the rain began to fall, making the track greasy and prompting a number of moments for Kimi Raikkonen, Alonso and Barrichello, who spun at Cotovelo.
Buemi had slightly more than a moment, losing it under braking and just missing Vitantonio Liuzzi as careened off backwards into the tire wall.
Webber improved again, as mentioned above, and so did Barrichello to go second quickest overall, just as the clouds ominously moved into position ahead of the second practice session, which airs live on SPEED at 1:00 p.m. Eastern.
Pos Driver Team Time Laps
1. Webber Red Bull-Renault 1:12.463 29
2. Barrichello Brawn-Mercedes 1:12.874 + 0.411 32
3. Vettel Red Bull-Renault 1:12.932 + 0.469 27
4. Kovalainen McLaren-Mercedes 1:12.989 + 0.526 25
5. Hamilton McLaren-Mercedes 1:13.048 + 0.585 25
6. Nakajima Williams-Toyota 1:13.067 + 0.604 21
7. Button Brawn-Mercedes 1:13.141 + 0.678 29
8. Rosberg Williams-Toyota 1:13.147 + 0.684 23
9. Sutil Force India-Merc. 1:13.232 + 0.769 23
10. Raikkonen Ferrari 1:13.321 + 0.858 24
11. Trulli Toyota 1:13.326 + 0.863 26
12. Heidfeld BMW Sauber 1:13.464 + 1.001 28
13. Buemi Toro Rosso-Ferrari 1:13.503 + 1.040 24
14. Kubica BMW Sauber 1:13.563 + 1.100 24
15. Fisichella Ferrari 1:13.619 + 1.156 23
16. Alonso Renault 1:13.787 + 1.324 28
17. Liuzzi Force India-Merc. 1:13.829 + 1.366 26
18. Kobayashi Toyota 1:14.029 + 1.566 27
19. Alguersuari Toro Rosso-Ferrari 1:14.040 + 1.577 38
20. Grosjean Renault 1:14.173 + 1.710 23