Formula 1 championship leader Oscar Piastri was fastest in sole practice for the Miami Grand Prix on Friday while McLaren teammate Lando Norris had to pit and jettison tools left in his car.
The Australian, chasing a third win in a row on Sunday, lapped on the quickest soft tyres with a best time 1:27.128 with Ferrari's Charles Leclerc next best but 0.356 seconds slower.
Red Bull's reigning champion Max Verstappen, arriving in Miami after celebrating the birth of his first child with partner Kelly Piquet, was third quickest and 0.430 off the leading pace.
The Miami round is a sprint weekend, with qualifying for the Saturday 100km race later on Friday instead of a second practice session.
Norris, last year's Miami winner who lost the championship lead to Piastri in Saudi Arabia two weeks' ago, was only 12th on the timesheets after red flags prevented him completing a lap on soft tyres.
He had to pit earlier after he found tools, including a torch, left in the cockpit when he took to the track for his first lap.
Stewards said they were investigating the team for releasing the car in an apparently unsafe condition, with the risk of a fine.
The session was stopped with four minutes remaining after Haas rookie Ollie Bearman hit the wall at Turn 12, before some drivers had completed quick laps on the soft tyres.
"I'm fine, sorry," the Briton said.
Norris and Haas's Esteban Ocon had earlier had a near-miss when the McLaren came up fast on the Frenchman going slow on the racing line at the end of the straight. That incident was also being investigated.
Williams' Carlos Sainz was fourth with teammate Alex Albon fifth and Racing Bulls rookie Isack Hadjar sixth.
Mercedes had George Russell seventh, ahead of Red Bull's Yuki Tsunoda and Mercedes Kimi Antonelli with Fernando Alonso 10th for Aston Martin.
Ferrari's seven-time world champion Lewis Hamilton was 13th, but again failed to get a lap in the soft tyres due to the red flags.