Ferrari's Fernando Alonso posted the fastest time in the first practice session at U.S. Grand Prix, followed closely by Red Bull's Mark Webber in a session first delayed by fog and then interrupted and shortened because the medical helicopter was late to arrive.

Alonso drove the Circuit of the Americas in 1 minute, 38.343 seconds. That was 0.0028 seconds faster than Webber, who has just two races left in his Formula One career.

Red Bull's Sebastian Vettel, who is chasing a record eighth consecutive victory in a single season, was 18th at 1:40.662.

Fog delayed the start by 40 minutes. The drivers were on the course for only about 15 minutes before the session was stopped until the helicopter arrived. The initial 90-minute session was condensed into about 45 minutes.