The first practice session for this weekend's U.S. Grand Prix got underway in wet conditions at the Circuit of Americas, with Mercedes' Nico Rosberg setting the fastest time of the morning.
Wet weather is forecast to disrupt this weekend's schedule and a heavy downpour one hour ahead of the start of FP1 gave the teams and drivers a taste of what is expected to come. However, air temperature as high as 26C and several cars on track saw track conditions improve as the 90-minute session wore on and the fastest laps were all set on intermediate tyres, with Rosberg's 1:53.989 over a second clear of Red Bull's Daniil Kvyat in second.
Lewis Hamilton, who can secure his third world title this weekend, was fifth fastest behind Daniel Ricciardo and Carlos Sainz, but with just four laps during the session the reigning world champion's time means very little at this stage. For the record, his closest rival in the standings, Sebastian Vettel, was just 0.02s off Hamilton after completing 10 laps in his Ferrari.
The wet conditions caught a number of drivers out under braking for some of the slower corners, but Felipe Massa was the only one to spin off after losing control of his Williams at Turn 9. The mistake was easily rectified with no damage done as Massa continued chasing a wet weather set-up, which has proved elusive for Williams all season.
McLaren was among the teams making the most of the session as Fernando Alonso put 18 laps on the new updated Honda engine and Jenson Button added 20 laps to the mileage of his old-spec Honda. However, Alonso's top ten position should not be treated on face value as he was one of the few drivers setting lap times towards the end of the session when conditions were at their best.