Sebastian Vettel has continued Red Bull’s relentless march in practice for the US Grand Prix at Austin, Texas.

The already crowned four-times World Champion nudged team-mate Mark Webber from the top spot in Practice 2 at the Circuit of the Americas track.

Vettel recorded 1:37.305s as Red Bull laid down the benchmark in the 90-minute session with Webber registering 1:37.420.

The Mercedes pair of Nico Rosberg (1:37.785) and Lewis Hamilton (1:37.958) were next.

Heikki Kovalainen has produced plenty of promise as the replacement for Kimi Raikkonen in the Lotus.

Unsurprisingly Kovalainen did the most running of the 22 cars, completing 41 laps and finishing with the fifth fastest time in 1:38.073.

Importantly Kovalainen finished three spots ahead of Lotus incumbent Romain Grosjean (1:38.255).

There were strange scenes in the opening practice session which had to be cut to 60-minutes as heavy fog restricted visibility with the medical helicopter unable to fly in the conditions.

When the session began Jenson Button had laid down the quickest lap before officials pulled out the red flag as it been discovered the helicopter had not yet landed at the track.

With 45 minutes remaining the session resumed however there was still no on-track action. Drivers had to wait until the helicopter landed trackside before launching into runs with just over 30 minutes remaining.

After all this Fernando Alonso set the fastest time in 1:38.343 to shade the early fast man Button.

See below for the Practice 2 result

See below for the Practice 1 result