Nico Rosberg clocked the quickest time during a damp first practice session for the United States Grand Prix.
Heavy rain during the early morning left the circuit wet but Intermediate tyres were able to be used throughout the course of the 90 minute session.
Rosberg set a time of 1:53.989 halfway through the session to finish comfortably clear of Red Bull duo Daniil Kvyat and Daniel Ricciardo.
Toro Rosso’s Carlos Sainz Jr. was fourth best, with World Champion Lewis Hamilton in fifth, 1.7 seconds behind pace setter Rosberg.
Sebastian Vettel was sixth for Ferrari, with Max Verstappen putting his Toro Rosso in front of the other SF15-T piloted by Kimi Räikkönen.
Fernando Alonso utilised Honda’s upgraded power unit, having bedded it in during practice in Russia, to finish the session in ninth, with Valtteri Bottas rounding out the top 10.
Bottas gave his Williams mechanics a scare when he locked up as he entered his pit box but the crew were able to leap out of the way of the FW37.
Felipe Massa spun en-route to 11th place while Jenson Button split Force India drivers Sergio Perez and Nico Hulkenberg.
Romain Grosjean set the 15th best time as he received an outing in the first session, with reserve driver Jolyon Palmer scheduled to run later, when conditions are expected to deteriorate.
Sauber test driver Raffaele Marciello finished three-tenths ahead of regular racer Marcus Ericsson, while Alexander Rossi began preparations for his home race by beating Will Stevens.
Pastor Maldonado completed just a slow installation lap during the preliminary stages of running as his Lotus developed a gearbox problem.