Austin: Championship leader Lewis Hamilton maintained his place at the top in Friday's second free practice session for this weekend's United States Grand Prix when he outpaced his Mercedes team-mate Nico Rosberg by just 0.003 of a second.
Hamilton had also been fastest in the morning session and his afternoon supremacy meant that he had now been fastest in 14 of the 17 second free practice sessions this year.
The two Mercedes men, separated by just 17 points in the title race, were more than a second clear of third-placed man, two-time champion Fernando Alonso of Ferrari.
Australian Daniel Ricciardo, winner of three races for Red Bull this year, was fourth ahead of Felipe Massa of Williams and Kimi Rakkonen in the second Ferrari.
Russian Daniil Kvyat was seventh for Toro Rosso ahead of Kevin Magnussen and his McLaren team-mate Jenson Button and 10th placed Nico Hulkenberg in a Force India.
Last year's winner, four-time world champion Sebastian Vettel, who is leaving Red Bull at the end of the season, was only able to complete a few installation laps at the end of the session following a gearbox change.
The German will have to start Sunday's race from the pit lane after changing the power unit on his Red Bull.