Lewis Hamilton headed the Ferrari of Fernando Alonso in a closely-fought
Friday practice at the Canadian GP.
Just 0.151 seconds covered the first three cars, with Ferrari's Felipe Massa in third place, while Sebastian Vettel was only 0.121secs further back.
Force India's Paul Di Resta was an impressive fifth fastest ahead of Sauber's Kamui Kobayashi.
McLaren's Jenson Button was ninth, managing only 18 minutes of the 90-minute session because of car problems.
BBC F1 technical analyst
“[McLaren] is a top team challenging for the championship. Changing the gearbox should be 30 minutes. It was nearly four hours. It's not good enough ”
Button suffered an oil leak in the
first practice session
and it took the team nearly four hours to fix it.
When he did take to the track, he concentrated on race preparation as he sought to make up lost time. He complained over the team radio of a lack of front grip.
Button said: "It's been a tough day. I didn't get many laps in and we didn't get a good feel. But we have the data.
"Lewis was very quick so the car is good. We missed out because we had a gearbox problem and an oil leak problem.
"We didn't really get any set-up work; I was just out there to get a feel for the circuit. But tomorrow is another day and we are still confident we can have a good weekend."
But BBC F1 technical analyst Gary Anderson said of McLaren's problems: "This is a top team with a world champion in it challenging for the world championship. It was nearly four hours.
"Changing the gearbox should be 30 minutes. It's not good enough.
"During that time Caterham rebuilt the car of Heikki Kovalainen, who hit the wall in first practice.
"McLaren discovered they hadn't fixed an oil leak, and they had to change the gearbox but that should be a half-hour job.
Did you know?
In the past decade, only three races in Canada have been won by the man who started on pole - Fernando Alonso in 2006 and Lewis Hamilton in 2007 and 2010.
"If you're trying to win the championship, you can't afford to make mistakes like this."
McLaren team boss Martin Whitmarsh said the problem was more complicated than it appeared.
"Jenson suffered an oil leak in this morning's session which necessitated the removal and re-fitting of his gearbox," Whitmarsh said. "Then, prior to this afternoon's session, we diagnosed another problem and as a result we had to change his gearbox yet again.
"Consequently, he lost a lot of running time - and then, when we finally got him out onto the track with only 18 minutes of P2 to go, he encountered quite a bit of traffic and was unable to get a decent run in the few laps available to him. Still, hats off to his mechanics, who did a splendid job to remove and replace the back-end of his car, not once, but twice, today."
McLaren managing director Jonathan Neale said that changing a gearbox takes "on average an hour and three-quarters up and down the pit lane" because of the complexity of modern F1 cars.
Mercedes driver Michael Schumacher was seventh fastest in the second session, split from team-mate Nico Rosberg in ninth by the second Force India of Nico Hulkenberg.
Sauber's Sergio Perez was 10th, ahead of the Red Bull of Mark Webber.
Webber's team-mate Vettel was pleased with his progress: "We used the super-soft tyres in P1 because we were a little bit afraid of the rain, which didn't come. We had a good day, we had decent laps, even with a little bit of a different approach in terms of when we put the tyres on. It looks to be very close."
Just as Kovalainen fell foul of the Circuit Gilles Villeneuve's unforgiving walls in the first session, losing control in Turn 9, Williams driver Bruno Senna suffered in the second session.
The Brazilian lost control at the final chicane and hit the barrier that has become known as the 'wall of champions' because of all the big name drivers who have crashed there.
Did you know?
Michael Schumacher has been on the Canadian Grand Prix podium 12 times - including seven victories - in 17 starts and has started on pole six times.
Senna said: "I pushed a bit too hard into the chicane. The kerbs are very aggressive there. I took a bit too much and I lost the car. It was a big crash and it caused a lot of damage."
Kovalainen said of his crash: "I haven't had a shunt for a long time, it was bound to happen one day.
"I was carrying a bit too much speed into that corner. I thought I'd got away with it, but the rear end snapped away and that was it. It was just a small error but it happens sometimes.
"We have got good mechanics. I don't think the chassis was damaged. It's just about replacing the two corners and we go again in the second session."
Hamilton, searching for his first win of the season,
looked in good form all day - he headed the first session from Vettel and popped to the top of the times whenever he was out on the track.
Hamilton and Button optimistic
The Briton suggested he could have gone even quicker had it not been for the mid-session stoppage following Senna's crash.
"I was out there pushing for quite a while on the option [super-soft] tyre. It is very, very difficult to put all the sectors together.
"Sometimes I would go quicker in one sector, and then would lose it in another sector. So I kept asking can I have one more lap, one more lap... and eventually I did get a good lap. Then the red flag came out, but I was already a couple of tenths up by then so that is positive for us."
Ferrari were trying out new parts - they had new rear bodywork and revised front brake ducts.
Massa started the first session with the new bodywork while Alonso stuck with the old, before they swapped later on. Both cars ran in the new spec in the second session. Only Massa ran the new brake ducts.
Anderson said: "From what I've seen so far, the developments look good - there are also some new front brake ducts on Massa's car that look effective. It will be interesting to see what parts are on which car in the second session."
Vettel was given a reprimand for an incident with Senna during the first session.
Senna was seen to be waving his arm at Vettel as the two cars approached the final chicane, with the Brazilian on the outside, and it turned out that the Red Bull had hit the Williams as it went past.
There appeared to be a second, less significant, incident later on, when Senna may have held up Vettel in retaliation.
Canadian Grand Prix 2012, day two
- Saturday, 9 June: Third practice 14:55-16:05 BST, live text and audio commentary BBC Sport website. Qualifying 17:55, live text and audio commentary BBC Sport website and Q3 online and BBC Radio 5 live. Qualifying highlights 22:30-23:45, BBC One
Canadian Grand Prix 2012, day three
- Sunday, 10 June: Race 18:45-20:50 BST, live text and audio commentary BBC Sport website and BBC Radio 5 live sports extra live. Race highlights 22:30-00:30, BBC One.