Sebastian Vettel remained on top during final practice for the United States Grand Prix as Red Bull again set the pace.
Having been first and second in FP2, it was another Red Bull one-two in the final session as Webber ended up 0.203s off his team-mate. However, Lewis Hamilton's late lap of 1:37.064 hinted that Mercedes may be able to take the challenge to Red Bull in qualifying this afternoon.
There was also a hint that Red Bull may be trying to nurse Vettel's car as he completed just 14 laps and race engineer Guillaume Roquelin told him over the radio at the end of the session: "Sorry mate we just wanted to minimise the amount of running on the car, that's why we called you in."
Nico Hulkenberg was an impressive fourth quickest for Sauber having topped the timesheets late in the session, with Romain Grosjean fifth and Jenson Button sixth. Nico Rosberg and Sergio Perez were the only other drivers to get with a second of Vettel's time, ahead of a clutch of cars separated by less than 0.3s.
Fernando Alonso was in that group a second off the pace, and he also endured a slightly nervous moment when approaching Pastor Maldonado's Williams during the high-speed first sector. Maldonado took a wide line to allow Alonso through at Turn 7 but the Ferrari suffered a moment of oversteer and had to slow, while Maldonado took avoiding action by running off track.
After his impressive first day in the Lotus on Friday, Heikki Kovalainen ended the session in 13th place, half a second off team-mate Grosjean and potentially facing a challenge to get through in to Q3.
Despite some early-morning fog, conditions were clear enough for running to get underway on time as Charlie Whiting ordered the medical helicopter to be present at the circuit overnight in order to avoid a repeat of Friday's delays.