US GP: Lewis Hamilton fastest in practice, Nico Rosberg troubled

The Mercedes driver was only fifth fastest based on pace on the slower medium-compound Pirellis, but in the final 10 minutes he bolted on the soft rubber and went fastest by almost nine tenths of a second.

Team-mate Nico Rosberg was second fastest having struggled with a brake problem until the closing stages of the session.

After initially lapping 0.884s slower on his first push lap on softs, with Hamilton failing to improve on his second attempt, Rosberg had the chance to close the gap.

He improved in the first and second sectors, but a scruffy final sector meant that Rosberg was only able to find a gain of one thousandth of a second.

With track temperatures relatively low, the session started slowly with Red Bull driver Daniel Ricciardo setting the pace while the field was on the mediums.

He outpaced Williams pairing Valtteri Bottas and Felipe Massa before the field switched to the softs.

It was the Williams drivers who ended up as best of the rest on qualifying performance, with Massa third fastest ahead of Bottas.

Ferrari driver Fernando Alonso, who briefly topped the times after becoming the first frontrunner to set a fast time on softs, ended up fifth ahead of Ricciardo.

Force India's Nico Hulkenberg was seventh, while Adrian Sutil put in a rare Sauber appearance in the top 10 with an impressive eighth fastest.

2007 and '09 world champions Kimi Raikkonen and Jenson Button were ninth and 10th, ahead of the second McLaren of Kevin Magnussen and the lead Lotus of Pastor Maldonado.

Toro Rosso endured a disappointing session, with Daniil Kvyat its quickest driver down in 15th after setting strong times on Friday.

This was possibly down to a loss of power, while team-mate Jean-Eric Vergne's session was cut short by an engine problem and ended up 17th behind Esteban Gutierrez.

Sebastian Vettel was slowest, having focused on race set-up work because he will start from the pitlane following the introduction of his sixth power unit.