Leclerc lapped the floodlit track with a best time of one minute and 34.802 seconds, 0.166 quicker than Williams’ Alex Albon.

Red Bull’s Yuki Tsunoda was third with four-times world champion teammate Max Verstappen fourth and Williams’ Carlos Sainz fifth.

Norris, who has opened up a 24-point lead in the championship with three rounds remaining, was 0.456 off the pace with Australian teammate and closest rival Oscar Piastri eighth.

McLaren have cautioned repeatedly in the run-up to Las Vegas that they are likely to face a tougher time at a track that has not favoured them in the past.

“I think this could be a tricky weekend,” chief executive Zak Brown told Sky Sports television halfway through the session, with Norris skimming the wall without damage and then running off later.

The opening session was on a dirty and unrepresentative track, on streets used by regular traffic, but Leclerc was on the pace from the start, with teammate Lewis Hamilton only 11th.

Racing Bulls’ Isack Hadjar was seventh fastest with his last lap of the session and Mercedes’ George Russell, last year’s winner, was ninth with teammate Kimi Antonelli completing the top 10.