Sebastian Vettel left it late, but then produced a blistering lap around the still slippery Circuit of the Americas to claim early honours in practice for the first USGP for five years.
The championship leader had trailed initial pacesetters Lewis Hamilton and title rival Fernando Alonso for much of the 90-minute session, but then showed that Red Bull is not about to cede any grounds to its pursuers by producing a 1min 38.125secs effort that took him fully 1.4secs clear of Hamilton and left the Briton with no time to muster a reply.
Hamilton and Alonso had traded times early on, the Spaniard edging back in front each time that his former team-mate opened a sizeable gap, before having to give best to the Briton as McLaren appeared to get a handle on the new 5.5km layout quicker than anyone else. Hamilton's team-mate, Jenson Button, filled fourth spot for much of the session, but ended the morning outing 2.4secs off the pace, with Alonso just a couple of tenths ahead and 2.2secs off Vettel.
The second Red Bull of Mark Webber rounded out the top five, but the Australian was just one of the drivers to overstep the limit of grip during the session. Right from the start, drivers were radioing back to the pits to report that they could not find traction on the new asphalt, but they gradually became accustomed to their challenging surroundings, which threw in elevation changes and a variety of corners to welcome F1 back to the United States.
Button and Hamilton both had moments where they took to the run-off, managed to avoid the list of spinners, which also included Heikki Kovalainen, Felipe Massa and Nico Hulkenberg. The Brazilian, however, produced the sixth-best time to slot in behind Webber, while Hulkenberg headed Kamui Kobayashi, Nico Rosberg and Sergio Perez at the foot of the top ten.
Paul di Resta was next up, ahead of the two Toro Rossos of Daniel Ricciardo and Jean-Eric Vergne, which found themselves in front of some illustrious company, including Abu Dhabi winner - and first man out in FP1 - Kimi Raikkonen and Michael Schumacher, who started the session with the rear bodywork of his Mercedes smouldering as the Brackley-based team reverted to an older spec exhaust in order to evaluate other areas of the car. Between the two world champions, Romain Grosjean and Pastor Maldonado filled 15th and 16th positions, while Bruno Senna struggled on a rare FP1 outing - having seen his seat handed to Valtteri Bottas for much of the season - eventually winding up in 22nd spot, behind everyone bar the lamentable HRTs, which ended the session 8.7secs and 10.4secs off the pace in the hands of Pedro de la Rosa and Ma Qing Hua.