US GP: Heavy rain in Practice Two but Lewis Hamilton dominates

Formula 1's opening day of practice at the United States GP was heavily restricted by torrential rain - but Lewis Hamilton still looked to be in ominous form as he comfortably topped both sessions.

Hamilton was more than a second clear of the field in both P1 and P2, which played host to the worst of the weather, despite only completing nine laps all day in the Austin deluge.

The Englishman can secure a fifth world title this weekend if he outscores Sebastian Vettel by eight points, and his championship rival suffered another nightmare day in his Ferrari.

Vettel, who struggled in the wet conditions, has been handed a three-place grid penalty after stewards decided he failed to 'slow sufficiently during a Red Flag period' during Practice One - in what is a crippling blow to his chances this weekend.

P1: Hamilton reigns in the rain
Vettel demoted three places

Rain showers are set to continue into qualifying at the US GP with the threat of flash floods in the state of Texas.

Conditions, however, are expected to improve in time for Sunday's race.

Rain wreaks havoc in P2
The conditions were so severe in Friday's second practice session that there was no track action at all for the first 50 minutes, before Toro Rosso sent Brendon Hartley out on track on full wet tyres.

But as the rain eased slightly to allow for intermediate running, it was Hartley's team-mate Pierre Gasly who appeared most at ease, faster than both Ferraris and Max Verstappen, the sole Red Bull to post a lap.

Vettel, meanwhile, was struggling to pick the optimum line in his Ferrari.

Hamilton soon emerged from the garage and, despite telling his Mercedes team that he wouldn't "learn anything" by driving in the rain, he quickly rose to the top of the timesheet.

Hamilton only posted one flying lap in the session, but his 1:48.716 was a second clear of closest challenger Gasly.

Verstappen, Fernando Alonso and Nico Hulkenberg completed the top five, while four drivers didn't head out on track at all.

Practice Three takes place at 7pm on Sky F1, with a crucial qualifying at 10pm.