Lewis Hamilton trails Kimi Raikkonen in Canada second practice
Ferrari's Kimi Raikkonen turned the tables on Mercedes driver Lewis Hamilton to set the pace in second practice at the Canadian Grand Prix.
The Finn was 0.215 seconds clear of Hamilton, fastest in the first session, and 0.265secs quicker than team-mate and title leader Sebastian Vettel.
Mercedes' Valtteri Bottas was fourth quickest, 0.11secs slower than Vettel.
Fernando Alonso, back after racing in the Indianapolis 500, was seventh after more Honda engine problems.
A battle brewing?
The top two teams appeared evenly matched, not only on their performance runs on the ultra-soft tyres, on which they set their fastest lap times, but also on the race-simulation runs later in the session.
Bottas and Raikkonen were the fastest of the drivers who did their long runs on the ultra-soft tyres and on their average times the Mercedes driver was quicker by a little less than 0.1secs.
Hamilton also ran on the ultra-soft tyre and was also 0.1secs slower than Bottas, although he had a disjointed run, featuring lots of slow laps, to the extent that it motivated Vettel, who was following him, to complain about his driving.
Vettel said: "I'm stuck behind Hamilton who is making mistakes and backing off."
But the four-time world champion played down the incident after practice, saying he knew Hamilton was just trying to get a clear lap.
Vettel said: "It was slippery and easy to do mistakes. I spun twice today. Mercedes looked good today but I think it will be very, very close, more or less like we all expect it, which is good."
Hamilton added: "The car is back to normal [after his struggles at the last race in Monaco] but it is still weak in a lot of areas and the Ferrari is still the quickest and with everything I am pushing currently, I can't beat the Ferrari's time."
Pressure builds on Honda
Two-time world champion Alonso's engine suffered a hydraulic leak after just one timed lap in the first session and missed the first hour of the second while Honda fixed the problem.
He did get out in time to do 17 laps and a couple of runs at the end of the session.
Team-mate Stoffel Vandoorne had a relatively trouble-free day but was only 19th fastest, his fastest time set on the slowest 'soft' tyre after he spun on his run on the quickest ultra-soft.
During the first session, Alonso was told by his engineer to stop on track. He pointed out that was he already at the hairpin, the last corner before the pit entry and it was easier to come back to the pits, but was ordered to stop.
He flung the impact-protection foam out of his cockpit as he climbed out and was given a standing ovation and cheers by the crowd in the grandstands.
"We are used to it," he told reporters on the way back to the pits.
The failure came as McLaren executive director Zak Brown again said that Honda had to up their game if the partnership was to have a future.
Two days after saying he had "serious concerns" about Honda, and a day after Alonso indicated he could leave McLaren at the end of the year if they were not winning by September, Brown told BBC Sport: "The plan right now is to have the Honda in the back of the car (in 2018) but some things need to happen between now and then for us to have the confidence we can be at the front of the field next year.
"We need to get competitive and show regular signs that we are getting competitive.
"Right now, we're not racing well, not finishing races and that can't happen any more.
"We are starting to work on the 2018 car so we need to make any decisions that impact 2018 by the summer break. Something needs to change.
"If you keep doing the same thing, you are going to get the same result. Maybe take some risks, do things they wouldn't normally do. You can't keep doing the same thing and expect things to change."
Asked if they had been discussing a customer engine supply with Mercedes, Brown said: "We have a plan B, a Plan C. We have some plans."
It was also a difficult Friday for Red Bull. Max Verstappen's car stopped on track with a technical problem causing an eight-minute red flag delay with 20 minutes of the second session remaining and ended up fifth quickest.
Team-mate Daniel Ricciardo suffered an engine problem early in the second session and was only 14th fastest.