Mercedes' Nico Rosberg clocked the fastest time of a tepid free practice one at the United States Grand Prix on Friday, as first wet then humid conditions made life difficult for the drivers.

The rain stopped falling approximately 15 minutes into the session, but with humidity at the Circuit of Americas track at approximately 90 per cent the track became sticky and greasy despite the surface drying out.

Subsequently, the drivers stuck to the wet or intermediate tyres in the tricky conditions and there was little to be learnt from a session in which no one was particularly keen to go too hard.

It was Rosberg who was top of the leaderboard, though, the German's time of one minute 53.989 seconds setting the benchmark.

Rosberg stated this week that he will not give up on the drivers' title despite needing a miraculous turnaround to overcome a 73-point deficit to team-mate Lewis Hamilton with four races remaining.

Indeed, Hamilton can wrap up the title if he wins Sunday's race and nearest rival Sebastian Vettel finishes lower than second. The Ferrari man's hopes are not helped by his decision to take on a fifth engine which will see him take a 10-place grid penalty for the race.

Hamilton could only finish fifth fastest, with Vettel a spot lower in sixth. The Red Bull duo of Daniil Kvyat and Daniel Ricciardo coped well with the conditions and were second and third fastest respectively, while Carlos Sainz (Toro Rosso) was fourth.

Top10

1.    Nico Rosberg (Mercedes): 1:53.989secs
2.    Daniil Kvyat (Red Bull): 1:55.224s
3.    Daniel Ricciardo (Red Bull): 1:55.592s
4.    Carlos Sainz (Toro Rosso): 1:55.667s
5.    Lewis Hamilton (Mercedes): 1:55.693s
6.    Sebastian Vettel (Ferrari): 1:55.710s
7.    Max Verstappen (Toro Rosso): 1:55.969s 
8.   Kimi Raikkonen (Ferrari): 1:56.326s
9.   Fernando Alonso (McLaren): 1:56.839s 
10.  Valtteri Bottas (Williams): 1:56.866s