Jenson Button topped the timesheets on the first day of pre-season testing despite a problem which sidelined him for much of the day. Meanwhile, problems for Mercedes too as Nico Rosberg's car catches fire following a wiring loom fault.

While all eleven teams were on duty today, Williams used its 2012 car, its 2013 contender not due to be launched until the first day of the forthcoming Barcelona test. All the cars that have been unveiled over the last week were in action, even the Caterham and Marussia that were only revealed this morning.

Button's morning's was compromised by a mechanical fuel-pump issue, which cost a couple of hours' track-time, but the problem was eventually rectified and the team was able to run productively for the remainder of the afternoon.

Button spent the first part of the day's programme running a lower-lip rake to complete some aero mapping work. The end of the day saw the team evaluate the effects of a series of mechanical set-up changes, using both the Supersoft and Hard tyres.

Both the aero mapping and the balance changes fell in line with the team's pre-test expectations. Button set his fastest time of the day on the hard compound.

Sergio Perez gets his first opportunity to drive a McLaren tomorrow, the knock-on effects of this morning's fuel-pump issue mean that he will begin his day by continuing today's initial aero and balance checks.

The aim for the afternoon is to conduct a series of longer runs - possibly incorporating live pit-stops into the mix if the team is satisfied with the day's initial progress.

Just 48 hours after Red Bull RB9 was unveiled in Milton Keynes, the new car took to the track with Mark Webber at the wheel, the Australian completing 73 laps. His best lap was the second quickest time of the day and left the Australian greatly encouraged ahead of his seventh season with the team.

"It was pretty good," beamed Webber. "As Adrian said at the launch, there haven't been big changes to the regulations this year and the car is an evolution of the one we finished with last season, so there were no big surprises. I think most of the drivers will sit back tonight and think today's times were pretty competitive.

"It was actually like a Friday practice session in some regards," he continued. "We started understanding the tyres and there were a lot of positives. There's a bit of housekeeping we have to get on top of but, other than that, it's been encouraging.

"The car feels similar to last year's, so the main difference is the tyres. With these tyres you're always on your toes. It was good that we had consistent temperatures today, so we got a lot of information and feedback to analyse, which is all good. Generally though, the car feels pretty good, so I'm happy."

"We had a very good day's running today," added Engineering Co-ordinator, Andy Damerum. "Being the first day of testing there's always a few nerves when the car goes out, but we had very few problems and Mark managed to get through just over 323km of running.

"We were able to get through about 90% of what was on the list for today. If I recall, this time last year we couldn't run in the morning because of fog, so this first day with the RB9 has been good. Tomorrow, we'll just crack on with the work load, which means more aero work and getting to know the tyres more."

At Lotus, Romain Grosjean was the pace-setter for much of the day, finally ending the afternoon with the third quickest time. The Frenchman completed 54 laps as the team went through its programme of shakedown and assessment.

"The feeling is good from the E21," said Grosjean, "it feels very similar to the E20 from behind the wheel, even if it does look different from the outside. Once again Enstone has produced a car that is quick from the very first lap.

"We spent a little bit more time than ideal in the garage today," he continued, "but that's normal in testing. I'm happy we completed 54 laps, and even happier that all of them were quick. We now have a good idea of the new tyres and we'll have some challenges from them; the grip level is there but performance does fall away with graining. That said, Jerez is a very specific track in this regard. The speed came easy today and we didn't respond to the other cars going faster in the afternoon. We should go even better tomorrow."

"It's great to see the fruits of our labours take to the track for the first time," added James Allison. "Everything has looked positive so far. The feedback from Romain has been encouraging and on the engineering side there have been no particular dramas of note. Overall it was a promising first day for this car and we hope to continue in this vein for the next days of testing."