Formula One championship leader Sebastian Vettel posted the fastest time ahead of archrival Fernando Alonso in the second practice session of the Spanish Grand Prix on Friday.
Alonso had the best time in the rain-affected first session, where Vettel drove more cautiously, but the Spaniard finished .017 seconds behind the German as sunshine bathed the Circuit de Catalunya for most of the afternoon's run.
Vettel clocked 1 minute, 22.808 seconds -- considerably faster than the 1:25.252 Alonso managed for Ferrari in the morning run.
Vettel's Red Bull teammate Mark Webber was third quickest and the Australian was .083 behind, with Finland's Kimi Raikkonen fourth fastest in his Lotus.
Saturday's qualifying promises to be highly competitive, with the top six in the second practice separated by .332 seconds. Ferrari's Felipe Massa was sixth, followed by Mercedes driver Lewis Hamilton.
Every driver apart from Max Chilton and Paul di Resta managed at least 30 laps, with Nico Rosberg getting 45 laps out of his Mercedes.
Vettel, who finished the first practice down in 19th place, flew out as soon as the afternoon session began.
The track design, with its long corners and changes in speed, offers a good test for the car upgrades providing it stays dry, and the afternoon conditions were perfect. Times dropped considerably as drivers tested out Pirelli's new modified hard tires.
Pirelli has made them slightly harder and longer-lasting after complaints they were wearing out too quickly, leading drivers to save up tires for race day and cutting short their practice runs. There appeared to be an issue with Di Resta's rear tires, however, when he went off track and banked onto the grass after completing 25 laps.
The upgrades are likely to prove especially crucial to McLaren as Jenson Button and Sergio Perez try to kickstart their bitterly disappointing seasons.
Perez tried out the car's new nose late in the afternoon session, which he finished in 13th place, a place behind Button, who did not do a timed lap in the first practice.
Button and Perez have managed only one fifth-place finish between them, and have had to clear the air after clashing during last month's Bahrain GP, where Button rebuked the Mexican for overly aggressive manoeuvers.