Ferrari's Fernando Alonso beat Mercedes driver Lewis Hamilton in a tight second practice session at the Canadian Grand Prix.
Alonso was just 0.012 seconds quicker than Hamilton as Lotus's Romain Grosjean took third ahead of Red Bull's Mark Webber and Mercedes' Nico Rosberg.
Ferrari's Felipe Massa was sixth from Red Bull's Sebastian Vettel. Lotus's Kimi Raikkonen was only 11th.
McLaren's Jenson Button finished ninth and Force India's Paul di Resta 12th.
The field looks very competitive and a tight battle for pole on Saturday seems likely - Vettel was just over 0.4secs slower than Alonso but lost three-quarters of that with traffic in the final sector of his fastest lap.
The first indications on race pace are that Ferrari and Red Bull are in the best shape, with Mercedes some way off their performance.
"The car feels pretty good and I feel like I'm pretty on it this weekend," said Hamilton. "I wouldn't say it's a big step forward. I still don't feel right in the car for some reason. I don't know if it's my seat.
"Today I was doing my belts up really tight, which I never do."
On the race-simulation runs on the super-soft tyres on which the drivers will start the race, Alonso set the fastest single lap - by nearly 0.5secs from Vettel - and had the best average, by 0.039secs from Vettel.
"It felt pretty good - always difficult to know what other people are doing, but all in all it was a good run," said Vettel.
"On the short run we have some room for improvement, Mercedes are very quick again. Overall, Mercedes are very quick, Ferrari looked competitive in long and short runs. I think they will be the biggest rivals.
"But never forget the Lotus. They can be good in the race by going further than everybody else."
The cool temperatures in Montreal led to a lot of drivers locking brakes and running wide at the chicanes and hairpin.
And both Red Bull drivers had off-track moments - Vettel ran off on to the grass on the exit of Turn One and Webber had a spin on the entry to Turn Six.
"Both drivers have found a good rhythm, the set-up changes seem to be working well," said Red Bull team principal Christian Horner. "Sebastian did not have a clean lap on the short runs - he got held up by Kimi - but it is still very positive for both drivers."
BBC F1 technical analyst Gary Anderson said: "I think Ferrari will be pretty happy. They are the ones who have come here with new bits - a new front wing and sidepod elements.
"They have tried to optimise their car for this track, they are pushing pretty hard after a difficult Monaco.
"But it's the usual teams at the front - Lotus will be up there with Mercedes, Ferrari and Red Bull and it will be an interesting qualifying session on Saturday. It's going to be very, very tight at the front."
The first session was run in mostly wet conditions, with Force India's Paul di Resta fastest in a brief period of dry running at the end.