Lewis Hamilton topped the timesheet of the Mexican Grand Prix's first practice session, the Mercedes driver edging Ferrari's Charles Leclerc and Red Bull's Max Verstappen.
Hamilton achieved his 1m17.327s fastest lap on the soft tyre, but Leclerc was just 0.119s adrift from the Briton while using the medium compound, a performance that bodes well for the Scuderia.
Verstappen's teammate Alex Albon concluded his session fourth, infront of Valtteri Bottas and Sebastian Vettel.
Friday's opening session kicked off under overcast skies, with a few damp patches still located around the Autodromo Hermanos Rodriguez.
The bulk of the field conducted its installation laps on intermediate tyres for good measure, although there was no real threat of rain on the horizon.
It took 25 minutes for a proper time to be put on the board, courtesy of Bottas. It was anything but a smooth run for the Finn however as he was seen battling his Mercedes in most corners.
Hamilton on the medium tyre briefly overhauled his teammate, followed by Vettel and the soft-shod Verstappen, with the latter breaking the 1m20s barrier.
But the Red Bull charger quickly relinquished the top spot to Hamilton once again, the Briton lowering the benchmark to 1m19.004.
The slippery nature of the track produced some near missed and forced a few drivers - including Vettel - off the circuit at Turn 1.
But Leclerc was well in control as he shot to the top of the timesheet with a sub-1m19s lap.
The initial burst of action, which lasted the better part of 15 minutes, was followed by a lull during which everyone took stock of their early performance and the conditions.
Over at Williams, George Russell was running the new front wing introduced by the team in Japan, while Nicholas Latifi focused on various mechanical tweaks as he enjoyed his fourth FP1 outing of the year.
When the action ramped up once again with just over 30 minutes to go, Red Bull's Alex Albon went fastest with a 1m17.949s.
But shortly after, the red flag was deployed following an off by Racing Point's Lance Stroll at the low-speed Turn 16.
The Canadian was fortunately able to drive his car back to the pits although the RP19 appeared damaged on its left side. The session remained halted as marshals tended to the outside barriers.
When the session resumed, Hamilton - now running on the soft tyre - promptly took the top spot with a 1m17.327s, but the Briton was closely followed by a medium-shod Leclerc and a soft-shod Verstappen.
Behind the usual top six suspects, Carlos Sainz upheld McLaren's status as best of the rest from Toro Rosso's Pierre Gasly and Daniil Kvyat, and Alfa's Antonio Giovinazzi.
While the action accelerated in the final minutes of the session, few were those who improved on their times.
Indeed at the front, position remained unchanged, with Hamilton and Mercedes leading the field from Leclerc, Verstappen, Albon, Bottas and Vettel.
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