Hamilton tops free practice; electrical issue sidelines Vettel

Red Bull's decision to change Sebastian Vettel's car for the Spanish Grand Prix backfired on Friday when an electrical problem sidelined the quadruple Formula One world champion for most of practice.

With race favourite Lewis Hamilton fastest in the morning session for dominant Mercedes, Vettel was forced to park up by the side of the track early on and with just four laps completed. Circuit de Catalunya marshals handed him a fire extinguisher as he inspected the car before hitching a ride back to the paddock on a scooter. "Due to an electrical problem that has damaged the wiring loom of Car No. 1, Sebastian will not be able to take part in FP2 (second practice)," said Red Bull said before the afternoon session started.

"The Team will use the time to fix it to be ready for FP3 (the final session before qualifying) tomorrow." Vettel, winner of the last nine races of 2013 and four championships in a row, has had a difficult start to the new V6 turbo era with Red Bull's engine partner Renault playing catch-up with Mercedes.

The last time the German was in action at a Spanish circuit, testing at Jerez in January, he spent most of his time in the garage watching mechanics work on the car. Hamilton, winner of the last three races and closing in on championship-leading team-mate Nico Rosberg, went from strength to strength with a fastest lap of one minute 27.023 seconds set six minutes from the end.

That was 0.868 quicker than Jenson Button, who was best of the rest for McLaren, and the impressive margin on a sunny morning further underlined the Briton's status as the man to watch. Rosberg, who had said on Thursday he just needed a "normal weekend" to regain the momentum, suffered a cooling issue that cut short his session. He was fifth fastest. Vettel's Australian team mate Daniel Ricciardo, who has made an impressive start with the team, was third.

In a bizarre early incident, a wing mirror on Sergio Perez's Force India broke off and was left flapping around on a wire. The Mexican completed the lap with it in his hand.