Championship leader Charles Leclerc topped the first F1 practice session in Miami, the Ferrari driver leading the reinvigorated Mercedes of George Russell and Red Bull's Max Verstappen.
All the front-runners set their fastest time on the soft compound tyre, with Leclerc concluding FP1 just 0.071s ahead of Russell while Verstappen was 0.179s adrift.
The frantic discovery session which featured several spins or half spins was interrupted by the first red flag and crash - and likely not the last - of the weekend, courtesy of Alfa's Valtteri Bottas.
Sergio Perez and Pierre Gasly rounded off the top five while Lewis Hamilton clocked in P8.
The most hyped-up race weekend in the history of F1 kicked off under clear skies and scorching temperatures, with air temps at 33°C and tracks temps set at 53°C.
There was a lot of talk about the Miami International Autodrome's track surface after it emerged that reparations to the tarmac had been necessary overnight.
So that's one area that will be under scrutiny this weekend.
Installation laps around the 3.363-mile, 19-turn circuit were also a learning exercise for F1 drivers who spent the early part of the session getting a feel for the layout.
As a reminder, Pirelli has opted for a middle-of-the-range tyre choice for this weekend, a conservative approach justified by the track's status as a new venue.
Aston Martin's Lance Stroll provided the first timed lap at Miami while Leclerc indulged in the very first half-spin. But that didn't deter the Scuderia charger – running on the medium compound – from setting the fastest time with a 1m33.440s.
Fifteen minutes into the session, Sainz briefly overhauled his teammate, but Leclerc reclaimed the top spot as he lowered the benchmark to 1m32.949s.
Running on the soft tyre, George Russell got within 0.01s of Leclerc, but it was Perez who popped to the top of the timesheet, at least until Sainz and Leclerc made it a Ferrari double treat shortly before the session reached its half-way mark.
A solid effort from Norris bounced the McLaren driver up to third, but Hamilton then sprung to second, splitting the two Ferraris.
However, minutes later Valtteri Bottas brought out the red flag after his Alfa's rear-end snapped in the middle of the long Turn 7 sweep.
The Finn slid off at a tangent and hit the outside wall, heavily damaging the rear wing of the C42.
After the stricken Alfa was evacuated from the track, the session resumed with 15 minutes left on the clock and drivers and teams likely ruing the lost time.
A push lap by Sainz resulted in a big spin for the Spaniard who miraculously avoided hitting the wall. But the Ferrari appeared to have picked up a front-right puncture that required a cautious return to the pits.
With ten minutes to go, things came together for a soft-shod Verstappen who put a 1m31.350s on the board to go over a second quicker than anyone else!
But more impressive was a blistering hot lap by Williams' Alex Albon who slotted himself into P2, 0.577s adrift from Verstappen.
But Russell then stole Albon's thunder with a strong charge to second, just 0.097s off the Red Bull pacesetter.
However, as the end of the session crept closer, Leclerc went top with a 1m31.098s on the softs, the Monegasque edging in the final pecking order an impressive Russell by 0.071s, proving that Mercedes' efforts to improve the pace of their W13 are so far fruitful.
Verstappen wrapped up FP1 early but stood P3 ahead of Perez, Gasly, Sainz, Albon, Hamilton, Hass' Kevin Magnussen and Daniel Ricciardo who rounded off the top ten.
Norris led the second half of the field, from Alpine's Fernando Alonso and Alfa's Guanyu Zhou. In the lower part of the group, Yuki Tsundoa, Mick Schumacher and Nicholas Latifi who were significantly slower than their respective teammates close out the running order.
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