Lewis Hamilton maintained his position atop the standings during final practice for the United States Grand Prix, but faced a stiffer challenge from title rival Sebastian Vettel.
Hamilton and Vettel traded quick laps during the one-hour session, held in warm and sunny conditions, and the Mercedes driver wound up with a 1:34.478.
Vettel finished just 0.092s behind Hamilton, as the leading contenders all registered their best efforts on the pink-banded Ultrasoft compound.
Valtteri Bottas and Kimi Räikkönen backed up their respective team-mates, 0.214s and 0.277s behind, with the Mercedes/Ferrari quartet closely matched.
Max Verstappen, who faces a 15-place grid penalty after taking on new engine components, was a low-key fifth, 0.625s off the pace, with Felipe Massa sixth for Williams.
Renault claimed seventh and eighth, as Nico Hülkenberg and Carlos Sainz Jr. were split by just 0.042s, the pair setting their low-fuel laps later in the session compared to their main rivals.
Daniel Ricciardo mustered only the ninth-best lap, ahead of Force India pair Sergio Pérez and Esteban Ocon, with Williams’ Lance Stroll 12th.
Fernando Alonso was unable to convert his Friday practice pace and slipped to 13th, in front of team-mate Stoffel Vandoorne, with Brendon Hartley in 15th spot, as he continued to get up to speed with Toro Rosso.
Kevin Magnussen took 16th, in front of Sauber pair Marcus Ericsson and Pascal Wehrlein.
Haas’ Romain Grosjean caused the Virtual Safety Car to be implemented when he spun into the gravel at Turn 7 midway through the session, while Daniil Kvyat managed just a handful of laps.
Kvyat complained of heavy steering on his STR12 and Toro Rosso detected a problem with the front of his car, which consigned him to the garage for the remainder of the session.
