BARCELONA, Spain (AP) Nico Rosberg was fastest in practice for the Spanish Grand Prix on Friday, continuing his dominance of Formula One.
Rosberg, who has won the first four races, led Ferrari driver Kimi Raikkonen and Mercedes teammate Lewis Hamilton in the afternoon session.
Rosberg was three hundreds of a second faster than Sebastian Vettel's leading time in the morning. Vettel was about a second off the pace in the afternoon, finishing behind Hamilton, who is using new parts to his power unit to try to avoid the mechanical failures that have plagued him this season.
Hamilton said it ''wasn't an easy day'' for him as he struggled with the car balance, but Rosberg had nothing to complain on his side.
''It was a good start for us with two good practice sessions,'' Rosberg said. ''I feel very comfortable with the car with some new parts added and they seemed to have worked well. Ferrari also look very strong around this circuit so I'm looking forward to Saturday's third practice session as well as qualifying.''
Vettel and Raikkonen were about half a second faster than the Mercedes drivers in the first session, although the times came on softer tire compounds that their rivals were not using at the time.
''In the end it is only Friday, so we need to be careful with our judgments,'' Vettel said. ''The first impression of our pace today was good. Whether we can confirm it tomorrow depends also on what the others were doing today. I believe we can make the step and be stronger tomorrow.''
Raikkonen had to abort a fast lap in the afternoon after the team detected a fuel system problem in his car. Both Ferraris have dealt with mechanical failures this season.
''It was only a small issue and by the end of the session we managed to do all that we wanted to,'' Raikkonen said. ''It's hard to say now where we are compared to our rivals, it was not a bad day, but for sure we can still improve.''
Ferrari hasn't started from the pole position in Barcelona since 2008, when Raikkonen was at the front.
Rosberg, who won from the pole in Spain last year, will be trying to win his eighth straight race, going back to last season. Vettel holds the record for most consecutive race wins with nine, which he achieved in 2013 with Red Bull. Two drivers won five in a row to start a season, Nigel Mansell with Williams in 1992 and Michael Schumacher with Ferrari in 2004. Schumacher also won seven in a row later that year.
Rosberg has a 43-point lead over Hamilton in the drivers' standings. Raikkonen is third and Vettel, who retired in two of the four races, is fifth.
Max Verstappen, who replaced Daniil Kvyat at Red Bull, was sixth fastest in the morning and eighth quickest in the afternoon, both times behind teammate Daniel Ricciardo. Kvyat was 12th fastest in the morning in his return to Toro Rosso, Red Bull's feeder team, and only 15th quickest in the afternoon, well behind teammate Carlos Sainz.
McLaren driver Fernando Alonso had a promising start to his home race, finishing the second session in seventh place, while teammate Jenson Button was 12th after struggling with handling issues in the morning and enduring a mechanical failure in the afternoon.
Haas driver Romain Grosjean was 13th fastest but said his car was a ''disaster'' and ''undriveable.'' Teammate Esteban Gutierrez was second-to-last in the afternoon.
British driver Jolyon Palmer, who was replaced by test driver Esteban Ocon in the morning session, had a rear tire blow on the front straight less than 30 minutes into the second session, prompting a red flag.
Spain is where most teams bring new updates to their cars, especially in aerodynamics. Mercedes and Ferrari were able to stay well ahead of the pace at the Circuit de Barcelona-Catalunya, which is where preseason testing took place over eight days in February and March.
Tales Azzoni on Twitter: http://twitter.com/tazzoni. His work can be found at http://bigstory.ap.org/content/tales-azzoni