Ferrari's Michael Schumacher and Felipe Massa set the pace in practice on Friday for the Italian Grand Prix. Schumacher, who is expected to announce his retirement after Sunday's race, and Massa - winner of the Turkish GP two weeks ago - clocked the second and third fastest times in the afternoon session.
BMW-Sauber test driver Sebastian Vettel led both the morning and afternoon sessions, although he won't be taking part in Sunday's race. Test drivers are usually fastest because the top drivers often experiment with different settings.
In the second session, Vettel timed 1 minute, 22.631 seconds. Schumacher was second in 1:23.138 and Massa third at 1:23.182. "It's a bit too early to make any snap judgments. It is only Friday and usually we see that things can change quickly during the weekend," Schumacher said. "Of course I want to win, but I don't think the gap we saw today will stay like this through the weekend."
Championship leader Fernando Alonso, who often underperforms in practice, was eighth with 1:24.577. Alonso drove his Renault slightly off track on two occasions.
"The gap always seems bigger on Friday. We look to experiment with our tires and fuel load," Alonso said. "I had a bit too much understeer today and that meant I couldn't attack the corners as I wanted to ... I am confident the car will feel good tomorrow." Alonso leads Schumacher by 12 points with four races remaining this season.
While Schumacher won't be able to catch Alonso in the drivers' standings this weekend, his Ferrari team is showing signs it could overtake the Spaniard's Renault outfit in the constructors' championship. Renault has a two-point lead over Ferrari.
While Alonso and Schumacher stayed in their garages, Vettel led the morning session with a time of 1:23.263. Vettel's Polish teammate, Robert Kubica, was second at 1:23.745 and Williams test driver Alexander Wurz was third in 1:23.868.
Vettel also led a practice session at the Turkish GP two weeks ago, when the German became the youngest official F1 driver at age 19.
McLaren-Mercedes' Kimi Raikkonen, still seeking his first win this season, posted the fourth fastest time of 1:24.037 in the morning, then dropped to sixth in the afternoon. Raikkonen is expected to be named Sunday as Schumacher's replacement at Ferrari next season.
Honda test driver Anthony Davidson had both of his sessions cut short early by mechanical problems, with his engine ending up in smoke and then flames. Teammates Rubens Barrichello and Jenson Button consequently skipped both sessions.
A third practice is scheduled before qualifying Saturday.