USGP: Rosberg tops practice 1

Nico Rosberg in the champion winning Mercedes topped the opening practice session for Sunday's United States Grand Prix at Austin.

A heavy downpour soaked the Circuit of the Americas just over an hour before the session began.

Fortunately the rain slowed with 45 minutes to the start, but the track was semi-wet throughout.

Rosberg’s teammate Lewis Hamilton, who will clinch his third world title this weekend, was 5th while Ferrari's Sebastian Vettel (2nd in points) and teammate Kimi Raikkonen were sixth and eighth.

Ferrari is running an updated power unit this weekend that will result in 10-place grid penalties for both drivers and will ensure Hamilton the title.

In the Manor slugs the duo Alexander Rossi, on home soil, and Will Stevens naturally brought up the rear with the latter almost eight seconds back.

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