Barcelona F1 testing: Nico Rosberg keeps Mercedes on top

After team-mate Lewis Hamilton ended up fastest on day three with a 1m20.558s, Rosberg led the way early on day four.

His best of 1m21.277s remained quickest for some time before the German and Fernando Alonso''s Ferrari started a sequence of short runs on the soft-compound Pirelli rubber.

Just after the session's halfway mark, Alonso managed a 1m21.024s lap, but almost immediately the Mercedes recorded 1m20.723s.

Alonso moved the mark to 1m20.606s in the final hour, only for Rosberg to make sure of the fastest time with 1m20.130s. He later set a 1m20.180s and has thus produced the two best laps of 2013 Barcelona testing so far.

Alonso eventually managed a 1m20.494s before switching to the super-soft, on which he failed to improve.

Almost a second behind the Ferrari came Jenson Button's McLaren. The 2009 world champion spent the early part of the session on harder rubber, but had a late run on unmarked Pirellis (suspected to be the soft compound) to end up third.

The midfield battle was close, with a tenth covering the Force India, Sauber and Williams times at one stage.

Sauber''s Nico Hulkenberg ultimately pipped Paul di Resta's Force India for fourth, with Pastor Maldonado completing the top six.

Reigning world champion Sebastian Vettel concentrated on the harder rubber compounds and was only seventh fastest.

Gearbox problems struck Kimi Raikkonen on his installation lap and his Lotus only made it back out in the closing moments of the session.

TODAY'S TIMES

Pos  Driver            Team         Time       Gap       Laps
 1.  Nico Rosberg      Mercedes     1m20.130s            53
 2.  Fernando Alonso   Ferrari      1m20.494s  + 0.364s  64
 3.  Jenson Button     McLaren      1m21.444s  + 1.314s  44
 4.  Nico Hulkenberg   Sauber       1m21.541s  + 1.411s  46
 5.  Paul di Resta     Force India  1m21.664s  + 1.534s  38
 6.  Pastor Maldonado  Williams     1m22.415s  + 2.285s  42
 7.  Sebastian Vettel  Red Bull     1m22.514s  + 2.384s  59
 8.  Charles Pic       Caterham     1m23.115s  + 2.985s  53
 9.  Jules Bianchi     Marussia     1m23.167s  + 3.037s  62
10.  Daniel Ricciardo  Toro Rosso   1m23.628s  + 3.498s  46
11.  Kimi Raikkonen    Lotus        1m24.396s  + 4.266s  7

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