Max Verstappen produced a late flier to narrowly set the pace for Red Bull ahead of McLaren's Oscar Piastri in the only practice session at the Miami GP before the competitive sessions begin on F1's second successive Sprint weekend.
Charles Leclerc's preparations for Friday evening's Sprint Qualifying - which is live at 9.30pm on Sky Sports F1 - and indeed the remainder of the weekend though suffered an early blow after the Ferrari driver completed just two full laps before spinning out of the session in a potentially costly error.
Verstappen had appeared to be having his own struggles around the 3.31-mile street track with the world championship leader twice running wide under braking as he sought to find the ideal balance with his RB20.
But the in-form Dutchman ultimately found the lap he needed to in the session's final moments and hit the top of the timesheet with a best time on the soft tyres of 1:28.595.
Encouragingly for the chasing pack, however, the early gaps around the wall-lined circuit were relatively close with McLaren's Piastri and Ferrari's Carlos Sainz ending just over a tenth adrift of Verstappen in second and third respectively.
In an unexpectedly expansive upgrade, McLaren revealed a suite of 10 different changes to their MCL38 ahead of the session - a package described as "astonishing" by Sky F1's Ted Kravitz.
Only Lando Norris has the full package on his car in Miami, with team-mate Piastri having access to around half the parts according to team chief Zak Brown. Piastri will carry the full package at the next race in Imola.
Piastri finished as the quicker of the two McLarens in the opening session with Norris' running initially delayed by a power-steering issue. The Briton eventually finished 16th fastest after putting 21 laps on the fully-upgraded car.
On the changes to the front of the McLaren, which include new front wing and revised suspension geometry, Kravitz said: "This is all about getting the front of the McLaren to work better in low-speed corners."
Mercedes, also running a number of upgrades on their W15 as they chase a much-needed step forward in performance, finished fourth and seventh quickest with George Russell and Lewis Hamilton respectively.
Lance Stroll was fifth quickest for Aston Martin ahead of Sergio Perez in the second Red Bull.
RB's Yuki Tsunoda was the quickest of the medium-tyre runners in eighth place, less than half a second off the pace.
Leclerc on the back foot ahead of Sprint Qualifying
Leclerc will go in to Sprint Qualifying - the session which sets the grid for Saturday's Sprint race - without any meaningful running under his belt after a small but costly error in the opening minutes of practice.
The Monegasque lost the back end of his car going through the left-hander at Turn 16 which leads onto the backstraight, spinning the car towards the inside wall.
Although the Ferrari did not make contact with the barriers and would have been able to continue without damage, Leclerc's attempts to make a spin turn did not go to plan and he ended up getting stuck sideways on the track - bringing out the red flag.
He did not rejoin the session thereafter when it resumed.
Sky Sports F1's live Miami GP schedule
Saturday May 4
3.25pm: F1 Academy Qualifying
4pm: Miami GP Sprint (race starts at 5pm)
6.30pm: Ted's Sprint Notebook
7.05pm: F1 Academy Race 1
8pm: Miami GP Qualifying build-up*
9pm: Miami GP Qualifying*
11pm: Ted's Qualifying Notebook*
Sunday May 5
6.05pm: F1 Academy Race 2
7.30pm: Grand Prix Sunday Miami GP build-up*
9pm: The MIAMI GRAND PRIX*
11pm: Chequered Flag: Miami GP reaction*
Midnight: Ted's Notebook*
*also live on Sky Sports Main Event
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