Sebastian Vettel snatched the fastest time from Fernando Alonso in the closing stages of day one of the latest winter test at Barcelona's Catalunya circuit.
On what may have been the hardest-to-read session of the winter so far, it took until lunchtime for the track to fully dry following Thursday's heavy rain. That meant the majority of drivers' fastest times were set during short exploratory runs late in the morning just as the circuit was at the tipping point of being ready for slick tires, before teams switched to longer runs in the afternoon.
Alonso's 1m25.485sec in the Ferrari during this period looked set to stand as the day's best, as the Spaniard switched to mid-range stints in the afternoon, covering between eight and 17 laps at a time, with a pace generally starting in 1m27sec then fading to 1m29sec by the end of his run.
Vettel completed relatively little running until the closing stages of the day, when he started a pair of short runs, lapping mostly in the 1m26sec during the first outing before re-emerging from the pits to blast in a 1m24.374sec with nine minutes to go.
That pace deposed Alonso by a full second, although it seemed Red Bull might have been using super-soft tires, as Vettel's times dropped off by 1-2sec for the remainder of his seven-lap run.
Toro Rosso's Jaime Alguersuari and Sauber's Kamui Kobayashi again set good times during relatively short runs to put themselves third and fourth. Both also caused red flags during the day – the Sauber running dry during a fuel consumption evaluation, and Alguersuari going into the Turn 4 gravel.
McLaren had another fairly quiet day, with Jenson Button sitting out much of the afternoon and taking fifth.
Paul di Resta was not able to get the Force India on track until the final few hours, though when he did so he was able to swiftly move up to sixth despite only managing 24 laps all day.
There were more glitches at Williams, where Rubens Barrichello – the first to get good pace out of slicks in the morning – caused a red flag just before the midday break and then was sidelined for nearly the whole afternoon while the team made a precautionary engine change. That left him seventh.
Eighth-placed Michael Schumacher spent his afternoon doing a race simulation in the Mercedes, covering a full grand prix distance broken up by quick pit stops. His pace tended to start in the 1m29sec/1m30sec region before going up by 2-3sec over the course of his 13-15 lap stints. His final total for the day was 89 laps, beaten only by Narain Karthikeyan in the 2010 Hispania (114 laps) and Jerome D'Ambrosio's Virgin (115). The latter pair were ninth and 11th, split by Lotus driver Heikki Kovalainen, who lost some track time with a water leak.
It was a difficult day for Renault. Its intention had been to let Vitaly Petrov have most of the session after Nick Heidfeld had completed some pit stop practice, but after the German's early appearance, Petrov had to wait until late afternoon before he could join in, as a KERS software glitch kept the car in the garage.
Pos Driver Car/team Time Gap Laps
1. Sebastian Vettel Red Bull-Renault 1m24.374s 37
2. Fernando Alonso Ferrari 1m25.485s + 1.111s 101
3. Jaime Alguersuari Toro Rosso-Ferrari 1m25.638s + 1.264s 57
4. Kamui Kobayashi Sauber-Ferrari 1m25.641s + 1.267s 78
5. Jenson Button McLaren-Mercedes 1m26.365s + 1.991s 77
6. Paul di Resta Force India-Mercedes 1m26.575s + 2.201s 26
7. Rubens Barrichello Williams-Cosworth 1m26.912s + 2.538s 52
8. Michael Schumacher Mercedes 1m27.512s + 3.138s 90
9. Narain Karthikeyan HRT-Cosworth 1m28.393s + 4.019s 116
10. Heikki Kovalainen Lotus-Renault 1m30.065s + 5.691s 54
11. Jerome D'Ambrosio Virgin-Cosworth 1m30.950s + 6.576s 116
12. Vitaly Petrov Renault 1m35.174s + 10.800s 20
13. Nick Heidfeld Renault 1m44.324s + 19.950s 27
All timing unofficial