Jenson Button beat Michael Schumacher and Lewis Hamilton to the fastest time in opening practice as Formula 1's return to Montreal got underway.
The reigning champion set a best time of 1m18.127s, 0.156 seconds ahead of Mercedes driver Schumacher, and 0.225s clear of his McLaren teammate Hamilton.
Though weather conditions were dry, bar a few spots of rain, all morning, drivers reported a very dirty and tricky surface on their exploratory laps, so half an hour elapsed before anyone tried setting a time – and it was halfway through the session before the quick men started lapping in earnest.
When they did, the morning quickly became a battle between Schumacher and the McLaren duo, with all three having turns in first place. McLaren spent much of the rest of the session holding a 1-2, but in the end Schumacher was able to get between Button and Hamilton. The former champion was clearly testing the limits, having a few near-misses under braking and the odd trip over the run-off areas.
Schumacher was not the only one to venture off-road, with Fernando Alonso, Vitaly Petrov, Bruno Senna, Hamilton and Sebastien Buemi among the others to go straight on at chicanes, and Pedro de la Rosa spinning his Sauber at the hairpin.
To complete a promising morning for Mercedes, Nico Rosberg moved the second car up to fourth with his final lap, just ahead of Red Bull's Sebastian Vettel, whose teammate Mark Webber was a low-key 14th.
2008 Montreal winner Robert Kubica (Renault) took seventh for Renault, ahead of Alonso's Ferrari, and the two Williams.
Lucas di Grassi was the only driver not to set a time, spending most of the session in the Virgin pits and then stopping out at Turn 6 not long after taking to the track.
Pos Driver Team Time Laps
1. Button McLaren-Mercedes 1:18.127 23
2. Schumacher Mercedes 1:18.285 + 0.158 19
3. Hamilton McLaren-Mercedes 1:18.352 + 0.225 19
4. Rosberg Mercedes 1:18.356 + 0.229 23
5. Vettel Red Bull-Renault 1:18.549 + 0.422 27
6. Kubica Renault 1:18.662 + 0.535 19
7. Alonso Ferrari 1:18.726 + 0.599 21
8. Liuzzi Force India-Mercedes 1:19.097 + 0.970 25
9. Hulkenberg Williams-Cosworth 1:19.282 + 1.155 31
10. Barrichello Williams-Cosworth 1:19.313 + 1.186 19
11. Sutil Force India-Mercedes 1:19.373 + 1.246 12
12. Massa Ferrari 1:19.511 + 1.384 21
13. Petrov Renault 1:19.549 + 1.422 24
14. Webber Red Bull-Renault 1:19.609 + 1.482 26
15. Kobayashi Sauber-Ferrari 1:20.186 + 2.059 33
16. Buemi Toro Rosso-Ferrari 1:20.320 + 2.193 27
17. de la Rosa Sauber-Ferrari 1:20.584 + 2.457 21
18. Alguersuari Toro Rosso-Ferrari 1:20.823 + 2.696 28
19. Kovalainen Lotus-Cosworth 1:21.869 + 3.742 24
20. Chandhok HRT-Cosworth 1:21.977 + 3.850 27
21. Trulli Lotus-Cosworth 1:22.543 + 4.416 12
22. Senna HRT-Cosworth 1:22.701 + 4.574 28
23. Glock Virgin-Cosworth 1:22.713 + 4.586 20
24. di Grassi Virgin-Cosworth 4
All Timing Unofficial