Highlights - Malaysian Grand Prix second practice (UK users only)
Lewis Hamilton enjoyed an encouraging Friday practice for the Malaysian Grand Prix as his McLaren set the pace in both sessions at hot and humid Sepang.
Hamilton's best lap of one minute 34.175 was 0.266 seconds faster than Red Bull's Sebastian Vettel in second.
Nico Rosberg got the better of Mercedes team-mate Michael Schumacher to finish third with the veteran back in fifth.
Defending world champion Jenson Button was fourth fastest, 0.363secs behind his McLaren team-mate Hamilton.
Hamilton led the way for most of a busy second session as the drivers battled gamely against the conditions, with track temperatures reaching 51 degrees and humidity levels hitting 60%.
The Toro Rossos of Jaime Alguersuari and Sebastien Buemi briefly led the way in the opening stages before Hamilton took control.
"It's not been a bad day," said the 25-year-old Englishman.
I was not 100% happy today, we still have to get a little bit quicker
Red Bull's Sebastian Vettel
"I had a good feeling in the car, probably the best feeling I've had in the car around this circuit.
"This is a special circuit, it's high-speed and flowing. It's about having the car flow and using all of the road and the kerbs.
"It's so hot, so it's hard on the tyres too. You have to drive it differently but my experience of the past should help," continued Hamilton.
But there were more problems for Red Bull, this time it was Mark Webber who suffered.
The Australian slowed down on his way into Turn Nine and pulled into the gravel trap after 30 minutes of the second session, seemingly because of an engine failure.
The incident ended Webber's session and Red Bull later said he had suffered a "loss of power".
"It was the engine, you never want your Friday disturbed and today's problem cost us quite a bit of track time," said the 33 year-old.
"But the car felt pretty good in the quick stuff and also at low speeds."
Mercedes seemed to pick up the pace in the middle section of the session, Rosberg demonstrated their desire when he overtook the Hispania of Bruno Senna at high speed going into the final corner.
The car is very good, very easy to drive on high fuel and low fuel
Ferrari's Fernando Alonso
Schumacher then briefly went top of the time sheets, but Hamilton snatched back top spot just 30 seconds later.
"We had a good programme," explained Hamilton, "We stuck to it and we are trying to get a good understanding of the tyres."
"There are some changes I need to make but nothing too serious. There are a couple that we will try and make for tomorrow but they are quite subtle.
"Hopefully the weather will be OK tomorrow. We don't know where everyone else is so it's important we don't get too excited and just do a good job tomorrow."
Vettel complained on team radio about a problem with his power steering after an hour of the session, but after easing off for a lap the German recovered to set the day's second fastest time.
"I was not 100% happy today, we still have to get a little bit quicker," said the German afterwards.
"The McLarens and the Mercedes look very quick, Ferrari I think have a decent long run pace so we need to see."
Ferrari spent most of Friday's two 90-minute sessions working on their race set-up, with both Fernando Alonso and Felipe Massa concentrating on long runs with heavy fuel loads.
"The car is very good, very easy to drive on high fuel and low fuel," said Alonso who clocked the seventh fastest time of the day.
"I'm happy with the balance, after Bahrain and Melbourne, this is a different track and hopefully tomorrow we can confirm our pace."
It is difficult to read too much into practice results as it is hard to determine what fuel levels and strategies the teams are running, but McLaren will be pleased to have performed well in both sessions.
Both Hamilton and Button benefitted from McLaren's 'F-duct' aerodynamic device to achieve impressive speeds on the two long straights at the Sepang circuit.
The system works by changing the airflow over the rear wing, which reduces the amount of drag and helps to give the McLaren an impressive straight line speed advantage.
But Button was not happy with the balance of his car, he reported under steer in high speed corners and told team radio that the rear end of the car was "moving around a hell of a lot" at the 120mph Turn Seven.
"It took me quite a while to get to grips with the car's set-up today, explained Button afterwards.
"I wasn't satisfied with it at first - I didn't really get a balance that I was happy with - but, towards the end of the session, it started getting better.
"That was encouraging and it was nice to see that we made some improvements right at the end because it was quite a way from what I wanted.
"We are steadily getting there, and it is starting to take shape, which is encouraging. We don't know what the weather's supposed to do tomorrow, but we'll deal with it whatever it is."
Highlights - Malaysian Grand Prix first practice