As ever at the start of the Canadian weekend, there were plenty of off-track moments as drivers explored the limits of the somewhat green track surface, with Hamilton, Toro Rosso’s Carlos Sainz and Williams’ Valtteri Bottas all surviving spins.
Hamilton's was perhaps the most dramatic, as he spun in the hairpin just as Rosberg arrived at the same corner. The two Mercedes were momentarily face-to-face, before the Briton took to the run-off area and spin-turned his Mercedes and waited to rejoin.
At that stage he was just 0.019s ahead of Rosberg, but his response to that error was to increase his margin to 0.415s even though he complained that he was losing time with lazy upshifts.
Hamilton's improvement left him on 1m 16.212s to Rosberg's 1m 16.627s, and in a worrying development for the non-Mercedes runners, the best of the rest in the wake of the Silver Arrows was Romain Grosjean's Lotus on 1m 17.721s, 1.5s down on Hamilton. Adding fuel to that particular fire, Nico Hulkenberg guided his Force India round 1m 17.871s for fourth.
It's not yet clear whether Ferrari are using their upgraded engine, and Sebastian Vettel didn't do a lot of laps early on his way to fifth fastest time of 1m 17.905s which left him just ahead of Williams' Felipe Massa on 1m 17.985s.
As expected, Renault were struggling on the long straights and their best runner was Red Bull's Daniil Kvyat in seventh on 1m 18.021s, which was fractionally quicker than Pastor Maldonado went in his Lotus as it stopped the clocks with 1m 18.026s.
Honda are running their uprated motor, and Fernando Alonso looked respectable in ninth on 1m 18.128s. Team mate Jenson Button however was initially troubled by a gearbox that stuck in second. The Briton didn't get going for the first 45 minutes, and ended up 15th on 1m 18.786s.
In between the two McLarens, Max Verstappen showed that his Monaco shunt hasn't had any effect on his speed as he took his Toro Rosso to 10th with 1m 18.257s. On top of his spin, team mate Carlos Sainz also struggled with poor engine driveability, and stopped at the end of the pit lane briefly when his car refused to disengage a gear, forcing his Toro Rosso crew to wheel him back to the garage. The Spaniard wound up 17th, on 1m 19.065s.
Valtteri Bottas finished down in 11th for Williams with 1m 18.325s, ahead of compatriot Kimi Raikkonen, who was 12th for Ferrari on 1m 18.439s. The top 14 was completed by Sergio Perez's Force India on 1m 18.503s and Daniel Ricciardo's Red Bull on 1m 18.775s.
Behind Button, Felipe Nasr was Sauber's faster runner on 1m 18.948s, while behind Sainz, Marcus Ericsson managed 1m 19.165s in the second C34. The Marussias were very closely matched, as Roberto Merhi headed Will Stevens with 1m 20.616s to 1m 20.624s.