Jenson Button and McLaren laid down an early marker on Friday when the Englishman topped the times in opening practice for Sunday's Spanish Grand Prix as drivers sweated over tyres for the race.
Button, the 2009 world champion, overcame problems with under-steer to clock the fastest time in the afternoon second free practice session in one minute and 23.399 seconds.
This gave him a comfortable advantage of more than one tenth of a second over defending double champion Sebastian Vettel of Red Bull at the end of an intriguing open day run in warm sunshine at the Circuit de Catalunya.
Button made the most of Pirelli's unforgiving softer tyres, much criticised for their lack of durability by other drivers including seven-times champion Michael Schumacher, as McLaren delivered a strong showing on the opening day of the European section of the 2012 season.
On a warm early Spring day, when the air temperature rose to 29 degrees Celsius and the track temperature to 43, Nico Rosberg, who won his maiden Grand Prix for Mercedes in Shanghai earlier this year, came third fastest ahead of 2008 champion Lewis Hamilton of McLaren.
"That was very different to winter testing here and a lot tougher on the tyres," said Rosberg.
"It has been a very challenging day first of all to see how to get the car right for qualifying and especially how to get it right for the race.
"I don't know where we are on tyre wear. We will have to look through the data now. Tyre management is going to be crucial here."
Asked about tyre degradation, Schumacher said: "That's a challenge. We have to find out more and analyse it to see what we did compared to the other guys. We have four of them (tyres) each time we go out and it's the same for everybody..."
Kimi Raikkonen, the 2007 champion, was fifth fastest.