BARCELONA, Spain - Lewis Hamilton set the pace for dominant Mercedes in the first practice session ahead of the 2014 Spanish GP on Sunday (May 11). Sebastian Vettel remained slow despite a Red Bull chassis switch.Hamilton's fastest lap of 1min27.023sec, set six minutes from the end, was 0.868 quicker than Jenson Button who was best of the rest for McLaren.The impressive margin at the Circuit de Catalunya further underlined Hamilton’s status as the man to watch after three wins in a row.VETTEL’S CAR WOESChampionship leader Nico Rosberg, who is four points clear of team mate Hamilton and had said he just needed a "normal weekend" to regain the momentum, suffered a cooling issue that cut short his session. He was fifth fastest.Vettel, who had a miserable pre-season test in Spain and has had a difficult four grands prix since then, kicked off the first European race weekend of the 2014 season with another setback.Vettel, winner of the last nine races of 2013, was using a different chassis to the one raced so far but he completed just four laps before pulling over with an electrical problem.Marshals handed him a fire extinguisher as he inspected the car before hitching a ride back to the paddock on a scooter.‘FULL ELECTRICAL SHUTDOWN’Team principal Christian Horner said: "We had a full electrical shutdown on Vettel’s car. We're not sure what caused it. It cut the radio and everything." Although the car was returned to the pits, the problem prevented Vettel from taking any further part in the morning session.Team mate Daniel Ricciardo, who has outqualified Vettel in three of the four races and passed him in the last two after the German was instructed to let the faster car through, was third fastest.Ferrari's Fernando Alonso, the local favourite for his home race after winning last year with plenty of banners in the grandstand urging him on, was fourth on the timesheets.With the opening long-haul races in Asia and the Middle East out of the way, all teams have brought updates to their cars and Friday's practice sessions were being closely watched for any signs of change in the pecking order.In a bizarre early incident, a wing mirror on Sergio Perez's Force India broke off and was left flapping around on a wire. Perez's completed the lap with it in his hand. 2014 Spanish Grand Prix: First practice1 Lewis Hamilton (Britain) Mercedes 1min27.023 2 Jenson Button (Britain) McLaren 1min27.891 3 Daniel Ricciardo (Australia) Red Bull 1min27.973 4 Fernando Alonso (Spain) Ferrari 1min28.128 5 Nico Rosberg (Germany) Mercedes 1min28.168 6 Kimi Raikkonen (Finland) Ferrari 1min28.337 7 Kevin Magnussen (Denmark) McLaren 1min28.423 8 Pastor Maldonado (Venezuela) Lotus 1min28.744 9 Sergio Perez (Mexico) Force India 1min28.779 10 Felipe Massa (Brazil) Williams 1min28.791 11 Daniil Kvyat (Russia) Toro Rosso 1min28.792 12 Nico Hulkenberg (Germany) Force India 1min28.828 13 Jean-Eric Vergne (France) Toro Rosso 1min28.859 14 Felipe Massa (Brazil) Williams 1min29.272 15 Adrian Sutil (Germany) Sauber 1min29.688 16 Jules Bianchi (France) Marussia 1min29.820 17 Romain Grosjean (France) Lotus 1min29.944 18 Giedo van der Garde (Netherlands) Sauber 1min30.440 19 Max Chilton (Britain) Marussia - Ferrari 1min30.748 20 Sebastian Vettel (Germany) Red Bull 1min30.942 21 Kamui Kobayashi (Japan) Caterham 1min30.997 22 Marcus Ericsson (Sweden) Caterham 1min31.421Stay with Wheels24 for the 2014 Spanish F1 GP weekend.