Nico Rosberg posted the fastest time ahead of Mercedes teammate Lewis Hamilton in the first practice session of the Spanish Grand Prix on Friday.

Rosberg, who is second in the standings behind defending champion Hamilton, clocked a best lap of 1 minute, 26.828 seconds - putting him .070 seconds clear.

Ferrari driver Sebastian Vettel, the only driver to have beaten Hamilton in a race this season, was third - .978 behind Rosberg - and his teammate Kimi Raikkonen was fourth fastest.

Carlos Sainz. Jr - the son of two-time world rally champion Carlos Sainz - gave home fans on the Catalunya circuit something to cheer with the fifth fastest time.

Hamilton has won three of four races this season and has clinched pole position in every race.

McLaren's problems with its Honda engine continued as Fernando Alonso and Jenson Button finished 15th and 16th, respectively. They were behind Susie Wolff, who was 14th quickest driving for Williams.

Button complained about his car's balance and Alonso - on the same track where he was injured in pre-season testing in February - did a full circle after coming out of one turn.

There is a second practice session later Friday.