Red Bull expectedly led the field in the opening practice session in Bahrain, but it was Sergio Perez who was the team's fastest driver.
Perez edged Aston Martin's Fernando Alonso who upheld the strong form displayed by the team in pre-season practice.
Reigning world champion Max Verstappen set the third fastest lap, 0.617s adrift from his teammate, while McLaren's Lando Norris was a surprise visitor among the top five despite his team's low-key performance in testing, the Briton finishing the session just ahead of Ferrari's Charles Leclerc.
As the field took to the track for the first official practice session of 2023, the only unfamiliar sight among the runners since last week's test was Alpine's pink A523, with the French outfit running its conspicuous livery in the first three races of the season.
Over at Aston Martin, Lance Stroll was back behind the wheel ready to get acquainted with his new mount after missing last week's preparations.
Air temperatures were a warm 27°C as everyone took to the track while track temps were set at 39°C.
Alonso led the early running but the Spaniard was quickly supersede at the top of the time sheet by Perez. The bulk of the field logically opted to run on the medium tyre, but Haas' chargers switched to the soft rubber early on.
It was a bit of a laborious start for Stroll whose car was left stranded in its garage, neutralized by an ignition issue. But the problem was swiftly solved by Aston's crews.
A little after the session had reached its half-way mark, Ferrari's Sainz completed a spectacular 360 after hitting a bump in the braking zone of Turn 9, fortunately with no other consequence but a ruined set of medium tyres.
Soft tyres became the norm as the session entered its final 15 minutes, but Perez remained out of reach, the Mexican confirming Red Bull's irresistible status as a favourite for top spoils for this weekend.
Lap times were of little relevance however given the high temperatures that will prevail in qualifying and on race day, while fuel levels were anybody's guess.
Nevertheless, Alonso confirmed Aston's pre-season form, although the Spaniard was 0.438s adrift from Perez, but almost two tenths ahead of Verstappen.
In fourth place, Norris suggested that McLaren's plight was perhaps not as bad as it has been made out to be.
Leclerc was Ferrari's fastest representative, the Monegasque edging Stroll who performed well on his return to active duty.
Haas' Kevin Magnussen made good use of Pirelli's soft compound by clocking in P7, just ahead of the Alfa Romeo pair of Zhou Guanyu and Valtteri Bottas.
Mercedes' first FP1 work session was capped by Lewis Hamilton rounding off the top ten, just 0.049s ahead of teammate George Russell.
Among the lower tier runners, Yuki Tsunoda was the fastest of the two AlphaTauri drivers, while Esteban Ocon preceded Pierre Gasly, but rookie Logan Sargeant had the upper hand against Alex Albon.
But a cooler FP2 session should provide a clearer picture of this weekend's hierarchy.
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