Lewis Hamilton ended Ferrari's domination of winter testing when he topped the times for the first time at Jerez in Spain today.
The McLaren rookie, settling into his second full test as an official race driver, outpaced Renault's Giancarlo Fisichella by more than one second - which suggests he was focusing on low-fuel, new tyre runs rather than consistent race pace.
However, Hamilton's day ended early, as he ran off the track, slightly damaging his car. The machine will be ready, though, for tomorrow's session.
Renault's Fisichella continued to get acquainted with the Bridgestone tyres. "I had a better second day, and I am beginning to find my feet with these new tyres," the Italian said.
"I am feeling more confident with the car, and I made good progress with the car in spite of some delay this morning owing to poor track conditions.
"The tyres are harder than what we have been used to, which means the grip is not so good. But I was expecting that, so it is not a surprise, and things are going well during this first session back in the car."
Rubens Barrichello was third quickest, leading the efforts for Honda Racing with teammate Jenson Button still unable to run because of the rib injury he picked up in a recent karting accident.
Honda's test driver Christian Klien, who was seventh quickest, caused the first red flag of the day when his RA106 stopped with mechanical problems shortly after 10:00am.
Nico Rosberg continued to get adjusted to Bridgestone's new 2007 rubber to set the fourth fastest time for Williams, while Ralf Schumacher was fifth overall for Toyota.
Felipe Massa was only sixth quickest, but his Ferrari team were surrounded by huge interest at the test as Kimi Raikkonen made a surprise appearance.
The Finn joined in the morning's technical meeting and then spent some time chatting to his future teammate.
Ninth fastest Nick Heidfeld, who was just slower than McLaren's Pedro de la Rosa, stopped on track just after 11:00am with a suspected electrical problem. His teammate Robert Kubica, who was 11th overall, also stopped just after lunch with a mechanical failure.
The only other incidents were at 11:00am, when Scott Speed spun off the track, and at 12:10pm, when Kamui Kobayashi stopped his Toyota on circuit with a transmission failure.
Pos Driver Team Time Laps 1. Hamilton McLaren-Mercedes (B) 1:18.684 78 2. Fisichella Renault (B) 1:19.685 63 3. Barrichello Honda (B) 1:19.784 111 4. Rosberg Williams-Toyota (B) 1:19.962 105 5. R.Schumacher Toyota (B) 1:20.024 70 6. Massa Ferrari (B) 1:20.046 60 7. Klien Honda (B) 1:20.055 99 8. de la Rosa McLaren-Mercedes (B) 1:20.141 64 9. Heidfeld BMW-Sauber (B) 1:20.167 97 10. Kovalainen Renault (B) 1:20.204 78 11. Kubica BMW-Sauber (B) 1:20.461 88 12. Badoer Ferrari (B) 1:20.556 107 13. Webber Red Bull-Ferrari (B) 1:20.596 89 14. Davidson Super Aguri-Honda (B) 1:20.701 112 15. Speed Toro Rosso-Cosworth (B) 1:21.134 59 16. Coulthard Red Bull-Ferrari (B) 1:21.276 78 17. Kobayashi Toyota (B) 1:21.292 53 All timing unofficial