Ferrari's Fernando Alonso narrowly beat Lewis Hamilton's Mercedes to the fastest time in Friday practice for the Canadian Grand Prix.
A totally dry afternoon session allowed teams to get on with the work stymied by morning rain, including testing the development Pirelli tyres, modified to try to eliminate recent delamination issues.
Alonso's team-mate Felipe Massa was fastest of all for a while using the revised tyres early on.
Hamilton then took over on soft tyres a few minutes later.
The Red Bulls were the first to try super-softs just before the session's mid-point.
That prompted a three-way battle for the top spot between Sebastian Vettel, Mark Webber and Hamilton, before Alonso jumped ahead of them all.
Alonso had looked on course to top the times on several other occasions earlier before making minor mistakes.
The Spaniard's 1m14.818s was 0.012 seconds ahead of Hamilton's effort.
Romain Grosjean grabbed third for Lotus, as Red Bull pair Webber and Vettel slipped to fourth and seventh.
They were split by Nico Rosberg's Mercedes and Massa.
Adrian Sutil put his Force India eighth.
Jenson Button had to stop slightly early in his McLaren due to gearbox sensor issues. He was still ninth quickest, sandwiched by Adrian Sutil's Force India and Daniel Ricciardo's Toro Rosso.
Paul di Resta also ran into mechanical trouble, a fuel feed problem on his Force India leaving him sat idle in the garage.
Pos Driver Team Time Gap Laps
1. Fernando Alonso Ferrari 1m14.818s 48
2. Lewis Hamilton Mercedes 1m14.830s + 0.012s 45
3. Romain Grosjean Lotus-Renault 1m15.083s + 0.265s 40
4. Mark Webber Red Bull-Renault 1m15.212s + 0.394s 46
5. Nico Rosberg Mercedes 1m15.249s + 0.431s 46
6. Felipe Massa Ferrari 1m15.254s + 0.436s 43
7. Sebastian Vettel Red Bull-Renault 1m15.280s + 0.462s 41
8. Adrian Sutil Force India-Mercedes 1m15.396s + 0.578s 43
9. Jenson Button McLaren-Mercedes 1m15.422s + 0.604s 29
10. Daniel Ricciardo Toro Rosso-Ferrari 1m15.566s + 0.748s 38
11. Kimi Raikkonen Lotus-Renault 1m15.599s + 0.781s 35
12. Sergio Perez McLaren-Mercedes 1m15.661s + 0.843s 39
13. Paul di Resta Force India-Mercedes 1m15.855s + 1.037s 22
14. Pastor Maldonado Williams-Renault 1m16.319s + 1.501s 46
15. Jean-Eric Vergne Toro Rosso-Ferrari 1m16.351s + 1.533s 38
16. Valtteri Bottas Williams-Renault 1m16.374s + 1.556s 40
17. Esteban Gutierrez Sauber-Ferrari 1m16.475s + 1.657s 45
18. Nico Hulkenberg Sauber-Ferrari 1m16.929s + 2.111s 35
19. Jules Bianchi Marussia-Cosworth 1m17.070s + 2.252s 41
20. Charles Pic Caterham-Renault 1m17.236s + 2.418s 35
21. Max Chilton Marussia-Cosworth 1m17.888s + 3.070s 45
22. Giedo van der Garde Caterham-Renault 1m18.392s + 3.574s 39