Around a sunny but windy Circuit of The Americas Sebastian Vettel headed Ferrari’s challenge in fourth place, with Red Bull’s Max Verstappen the only other man to finish within a second of Rosberg’s P1 time.
The Force Indias of Nico Hulkenberg and Sergio Perez were sixth and seventh respectively, followed by the McLarens of Jenson Button and Fernando Alonso. Kimi Raikkonen in the second Ferrari completed the top ten.
After the Ferraris of Vettel and Raikkonen had set the initial pace, with 1m 38.892s and 1m 38.930s on the supersoft Pirelli tyres, Verstappen took over with 1m 38.541s on soft rubber before Rosberg went ahead on the same tyre with 1m 38.082s. Hamilton’s effort fell short of his team mate’s as he went second with 1m 38.394s, but interestingly Mercedes had split their tyre strategy and he was running the mediums. Ricciardo also got in on the act, first with 1m 38.675s for fourth, then 1m 38.529s for third. Vettel then took second with 1m 38.178s, still on the supersoft.
On the softest rubber Verstappen then improved to 1m 38.258s to go third, as Rosberg on the same tyre clipped down to 1m 37.358s which remained the fastest lap of the session. Ricciardo too ran supersofts as he climbed to second with 1m 37.552s, leaving Hamilton - also on the red-marked rubber - third with 1m 37.649s.
Thereafter it was a case of doing long runs, with the Red Bulls both looking very strong on softs, Rosberg running them too, and Hamilton doing a good job on the mediums.
Behind the top three, Vettel ended up fourth ahead of Verstappen, with Hulkenberg’s 1m 38.508s leaving him just ahead of Force India partner Perez’s 1m 38.568s in sixth and seventh.
McLaren had a good afternoon, as Button just pipped team mate Alonso, 1m 38.713s to 1m 38.801s, as Raikkonen completed the top 10 with 1m 38.865s after struggling with his SF16-H.
Once again there were spins at Turn 18, for Manor’s Esteban Ocon and Toro Rosso’s Carlos Sainz, Renault’s Jolyon Palmer spun again, at Turn 8, and Rosberg went off briefly at Turn 19. There was also further debris; the session was briefly red-flagged at 14.54 so some carbon fibre could be cleared in Turn 4, and later Esteban Gutierrez’s Haas divested itself of some of the same material.