Red Bull's Max Verstappen drew first blood in Bahrain in Friday's first practice session, the Dutchman putting in a late charge to edge Mercedes' Valtteri Bottas.
The reigning world champions appeared in better form at the outset in FP1, with Lewis Hamilton concluding the session fourth fastest just behind third-place McLaren man Lando Norris.
Conditions at the outset of the first free practice session of the season were an improvement over those that drivers encountered in pre-season testing, with low wind and no sandstorm in sight.
However, a dusty track required drivers to tiptoe into the 60-minute session. Alpine's Fernando Alonso, F1's returnee, had the honour of being the first driver to take to the track.
The Spaniard was followed by teammate Esteban Ocon, AlphaTauri's Yuki Tsunoda and Ferrari's Carlos Sainz, and the remainder of the field in random order.
With practice sessions shortened from 90 to 60 minutes this year, drivers lost no time getting down to business and there were none of the customary lulls in the running.
As if Mercedes' pre-season testing troubles were relegated to a distant past, Hamilton set the early pace, with Verstappen snapping at the Briton's heels and Bottas and Perez also close behind, with the quartet running on Pirelli's soft compound as most of the field.
The halfway point of the session came and went with no change among the front-runners. Among the laggards, McLaren's Daniel Ricciardo had yet to complete more than one lap, as was the case for both Haas and Alpine drivers.
Hamilton was seen having a moment at the final corner just before Norris lit up the timing screen with a 1m31.897s on softs that cleared the Mercedes driver by 0.317s.
Shortly after, Ricciardo sprang into action, slotting himself among the top five. But a good effort from Leclerc pushed the Ferrari driver up to P2, 0.096s adrift from Norris. Sainz followed suit, although the Spaniard was a few tenths behind his teammate in P5.
Meanwhile, as the session entered its final 15 minutes, Gasly popped up in P3, the AlphaTauri charger also leading the lap count at that point.
The action intensified in the closing stages of FP1, with Bottas and then Verstappen stealing Norris' thunder.
The Dutchman held his own in the final minutes, thus concluding the first practice session of the season at the top of the time sheet, with an 0.298s advantage over Bottas and alittle over half a second over Norris.
Hamilton and Leclerc completed the top five, a performance that likely satisfied both teams while Perez was P6, 0.677s drift from Verstappen.
Gasly, Sainz and Ricciardo rounded off the top ten, with Alfa Romeo chargers Antonio Giovinazzi and Kimi Raikkonen finishing just outside the half.
Aston Martin's Sebastian Vettel and Lance Stroll were grouped together in P12 and P13, preceding Yuki Tsunoda and the Alpine duo of Ocon and Russell, the French outfit shying away from any performance runs to focus on aero work during the session.
Williams' George Russell ended his maiden session of 2021 P17; just ahead of Nicholas Latifi, with Mick Schumacher and Nikita Latifi making up the rear.
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