Title rivals Max Verstappen and Lando Norris finished the only practice session at the United States Grand Prix in third and fourth place.
Carlos Sainz set the pace for Ferrari teammate Charles Leclerc at the Circuit of the Americas in Austin.
Sainz was 0.021 seconds ahead of Leclerc and 0.253 seconds faster than Verstappen, whose time was set earlier in the session than Ferrari and McLaren when the track would have been slower.
Norris, who starts the weekend 52 points behind Verstappen in the championship, was 0.013 seconds slower than the Dutchman.
Mercedes driver Lewis Hamilton, who made a high-speed spin in turn four earlier in the session, finished fifth, ahead of teammate George Russell, who himself spun in turn one.
Mercedes is among the teams with a significant upgrade to their car, along with Red Bull, McLaren and Aston Martin.
The weekend started with a controversy over a device on the Red Bull that allows you to adjust the height of the front of the floor.
Red Bull has responded by pointing out that McLaren has made changes to the rear wing – an extension of discussions they had with governing body the FIA ​​after the Azerbaijan Grand Prix where it was seen to deflect on the straight.
A McLaren spokesperson said: “As previously stated, McLaren proactively offered to make some minor adjustments to our rear wing following the Azerbaijan GP. We have made varying degrees of minor adjustments to all our rear wings since Baku to prevent further problems from arising in this area. .”
Liam Lawson, who has replaced Daniel Ricciardo at RB, was 13th, 0.130 seconds behind teammate Yuki Tsunoda in 10th.
This is a ‘sprint’ weekend, with a shorter race on Saturday. Qualifying for this is on Friday at 10.30pm BST, with the sprint on Saturday at 7pm.
