United States GP: Ferrari's Carlos Sainz takes top spot in opening practice
Ferrari's Carlos Sainz took top spot in opening practice for the United States Grand Prix ahead of double world champion Max Verstappen.
Lewis Hamilton finished third after his Mercedes team brought a number of upgrades to the Austin's Circuit of the Americas - and the British driver finished half-a-second off the pace.
Verstappen claimed his second consecutive title at the rain-hit Japanese Grand Prix a fortnight ago.
But the Dutchman's superb achievement has been overshadowed by Red Bull's breach of last year's £114million budget cap.
Formula One's governing body, the FIA, has tabled a punishment, with the Red Bull hierarchy now determining whether to accept it, or challenge the verdict.
On track, Red Bull arrive in Texas undefeated in their last seven outings, and Verstappen finished the first action of the weekend 0.224 sec adrift of Sainz.
Sainz's team-mate Charles Leclerc sat out the opening running with the Italian team's academy driver Robert Shwartzman handed his grand prix debut. The Israeli finished 16th, two seconds behind Sainz.
Mercedes are trialling a new front and rear wing and revised floor at the 19th round of 22, with Hamilton still seeking his first victory of the season.
The seven-time world champion was 0.475 sec slower than Sainz. His team-mate George Russell finished seventh.
Sergio Perez finished fifth for Red Bull, but the Mexican driver is facing a grid penalty on Sunday for exceeding his number of allocated engine parts.
A number of young guns were fielded in the first action, with Alex Palou 17th for McLaren, one place ahead of Williams' junior driver Logan Sargeant.
Antonio Giovinazzi, dropped by Alfa Romeo at the end of last season, was back in action as a practice stand-in at Haas.
But the Italian hit the wall at Turn 6 and was ruled out of the remainder of the action with clutch damage, having completed just four laps.