Highlights - Canadian GP practice two (UK users only)
By Andrew Benson
BBC Sport in Montreal
Red Bull's Sebastian Vettel headed Ferrari's Fernando Alonso in second practice at the Canadian Grand Prix as McLaren failed to repeat their early pace.
McLaren had lived up to their billing as pre-race favourites with an impressive showing in the first, morning, session.
But Lewis Hamilton and Jenson Button were seventh and 11th in the afternoon.
Nico Rosberg was third for Mercedes ahead of Vettel's team-mate Mark Webber and Felipe Massa's Ferrari.
Vettel's fastest lap was a one minute 16.877 seconds, only 0.086secs faster than Alonso.
But it was noticeable how much easier the Red Bull appeared to be to drive than the Ferrari.
Red Bull duo concerned over tyres
"It's looking good, I feel comfortable in the car," said Vettel. "It's very slippery - for two years we haven't had a race here and the circuit needs time but it was already much better in the afternoon."
Webber added: "It'll be a hard fight on Saturday with everyone, but the car ran really well today and we'll see what happens tomorrow."
Alonso had a number of off-course moments, and the Ferrari appeared very twitchy in the braking zones for the corners.
Nevertheless, it was notable that the Spanish double world champion set his fastest time on the same set of tyres and on the same run on which he had previously slid off the track on to the grass at Turn Four.
Highlights - Canadian GP practice one
"Overall the car is OK but in Istanbul I remember we were fourth, fifth in Friday practice and in qualifying we were out of Q2 so we need to stay focused and concentrated on Saturday because everything can change when everybody goes flat out in qualifying," said Alonso.
"We have been using these sessions to try the tyres, to work on the brakes - this circuit is very hard on the brakes.
"We just concentrated on the race situation and we didn't pay attention to the times because we know on Saturday everything can change."
The Spaniard said the car's occasional wayward behaviour had been caused by Ferrari experimenting with their brakes.
Button unsure over slow pace
"We know this is one of the key parts in the circuit, in terms of performance, because we know how much time you can gain in the braking zones," he added.
"We have been working on the brakes all day long, trying different materials and cooling levels, etc to make the car ready for Sunday. On those occasions it was not easy sometimes to brake, but I think it will be fine for Saturday."
In the first session, Button's fastest lap was a 1:18.127, heading Mercedes's Michael Schumacher by 0.158secs and Hamilton, in third, by 0.225secs.
Vettel and Webber were only fifth and 14th in the morning session.
"This morning was good and this afternoon wasn't so we have to work out why," said Button, who trails championship leader Webber by five points in the drivers standings.
"We were very competitive this morning - maybe we were running less fuel than most people - but this afternoon we struggled with the balance a little bit, instability on braking and corner entry was an issue on new tyres.
"Then on the long runs, it's a little bit emotional out there - the tyres aren't lasting very long.
"I ran with the option tyres with heavy fuel at the end and it grained so much I came in and put the prime on and then went out and I was two or three seconds quicker than the other cars who were on options.
"We think possibly we're a little bit too quick on the straights."
Looking at our consistency we're struggling a little bit; maybe we're not running enough downforce."
Hamilton not happy after second practice
McLaren are strongly tipped to win the race, and perhaps even finish one-two for the second race in succession, because their car design is in theory best suited to this track.
Particularly, they have mastered the so-called 'F-duct' aerodynamic device, which they introduced at the start of the season and which has since been copied by several other teams.
The 'F-duct' increases straight-line speed by 'stalling' the rear wing - i.e. stopping it working - on the straights which are such a dominant part of the lap time here at the Circuit Gilles Villeneuve.
That allows them to run more downforce than they would otherwise be able to, increasing the car's speed in the corners, without sacrificing its pace on the straights.
The track, on the Ile Notre Dame in the St Lawrence Seaway, is fundamentally a series of straights linked by chicanes, with a hairpin at either end.
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There are virtually no fast corners, where the Red Bulls have been so strong this season.
And while other teams - including Ferrari, Mercedes and Force India - have their own versions of the 'F-duct', none of them have optimised it to the extent McLaren have.
But after second practice Hamilton sounded pessimistic about his team's chances over the weekend.
"I'm not happy with the way this afternoon went - in general, the track has been incredibly difficult to drive," said Hamilton, who claimed his first grand prix victory here in 2007.
"It's very difficult to switch the tyres on and get heat into them. It's just like being on an ice rink out there, it's so slippery.
"It's such a huge difference to when I was out here before, we had great grip then and the track just got better and better but for us we're struggling a little bit, that's for sure.
"We're losing out everywhere. We're not pulling away down the straights, we have quite a lot of bottoming but there are areas we can improve on. We'll just have to do a big debrief now and figure out where we want to go with the car tomorrow. It's a bit of an unknown.
"We tried a few things and the car was as bad if not worse."