Fernando Alonso set the pace in front of his home fans in a wet-dry first practice session for the Spanish Grand Prix.
Alonso's time of 1:25.252 left him just 0.2s clear of Ferrari team-mate Felipe Massa at the Circuit de Catalunya, with Jean-Eric Vergne third quickest ahead of Romain Grosjean and Adrian Sutil. Having been faced with a wet start, the drivers all set their best times in the closing minutes as the track dried out and it was Alonso who took top spot from Massa with his final flying lap.
Vergne was the first driver to switch to slicks, resulting in his high position, but did have a few off-track excursions as the track remained slippery away from the racing line. Lewis Hamilton was sixth quickest for Mercedes, but with teams all trying to analyse new parts and updates little can be taken from the times as the Red Bull pair of Sebastian Vettel and Mark Webber ended the session in 19th and 20th respectively.
McLaren only completed 12 laps in total between its two drivers, with Button bottom of the timesheets as he failed to set a time on any of his six laps having only emerged from the pit lane with half an hour of the session to go. Despite the team trying to recover from a poor start to the season, the limited running was due to a lack of spare new parts at the circuit.
The majority of the first hour of running was conducted on the intermediate tyre - though some drivers opted for full wets during the opening ten minutes - as the track was wet following a heavy shower in the hour prior to the start of the session. While times were impossible to read in to in such conditions, the teams still carried out plenty of running in order to gather data to analyse their respective upgrades.
With teams needing to run in the wet, there were numerous off-track moments and Grosjean spun at Turn 10 while Maldonado ran wide at the same corner. As the track dried, Massa also had a high-speed moment when he went off on the exit of Turn 2 but was able to recover through the gravel.
Heikki Kovalainen's second practice run in a reserve capacity for Caterham was affected by a gearbox leak early in the session, but he recovered to complete 14 laps. He ended the session 0.3s ahead of team-mate Giedo van der Garde in an updated CT03 featuring a vanity panel over its stepped nose.