Lewis Hamilton set the fastest time in a soaking wet final practice session for the U.S. Grand Prix, which could end up setting Sunday's grid if qualifying is rained off.
Formula One's rules state that the final practice standings will be used to decide the grid if qualifying cannot take place ahead of the race, which added extra importance to the morning's session. All the drivers headed out on track in search of a quick time, with the FIA enforcing the use of full wet tyres in the treacherous conditions. Fans, however, were told to stay at home until midday, meaning the session -- which was busy even by the standards of a dry final practice -- unfolded in front of empty grandstands.
Hamilton, who can wrap up his third world title this weekend, was over 0.8s quicker than any of his rivals as a combination of driving skill, a sorted car and good timing to catch the best of the conditions resulted in a hugely impressive lap time. Hamilton's closest title rival Sebastian Vettel was second fastest as six different cars made up the top six places in the standings, while Hamilton's team-mate Nico Rosberg could only manage ninth in the conditions. However, regardless of whether FP3 decides the grid, both Ferraris are due to drop ten places on the grid due to engine penalties.
If proof was needed of how bad the conditions were, Rosberg provided it on just his second lap when he lost the rear of his car in Turn 3 and aquaplaned into the barriers. He damaged his front wing but was able to return to the pits before rejoining the action ten minutes later, although he could not match Hamilton when the track conditions were at their best.
The two Ferraris led the way after the first ten minutes of running, but a brief respite in the conditions around the half hour mark saw times start to improve again. Hamilton was keen to take advantage of the marginally improving conditions and became the only driver to set a time under 2 minutes, which stood as the fastest time for the rest of the session. Ferrari reacted by heading back on track, but Vettel spun twice in the space of two laps as he attempted to lower his time, meaning he missed out on making the best of the faint racing line that was emerging between the puddles. As the rain intensified in the final 20 minutes there was little to be gained from further running and the standings did not change before the chequered flag.
Qualifying is due to take place at 13:00 local time, but the FIA holds the final call on whether to postpone or cancel the session if conditions continue to worsen. It is also possible that qualifying could take place on Sunday morning ahead of the race, meaning only the weather can decide whether FP3 carries any true significance in the story of the 2015 title.