Ferrari's Charles Leclerc edged Red Bull's Max Verstappen by 0.116s in Friday's opening practice for the Saudi Arabian Grand Prix.
The Monegasque secured his spot at the top of the timesheets late in a session dominated from the outset by Verstappen.
Behind the leading duo, Alfa Romeo's Valtteri Bottas was third, with Carlos Sainz and Pierre Gasly rounding off the top five.
Mercedes lagged its direct rivals in FP1, with Lewis Hamilton clocking in P9 and George Russell concluding his afternoon work session a lowly P15.
Formula 1 has set up shop along the shores of the Red Sea just fifteen weeks after its maiden visit to Jeddah back in December.
And the fastest street track on the calendar has undergone a few changes, mainly to improve the venue's safety by increasing the drivers' sight line in the fast twisty sections of the circuit.
As reported earlier today, Nico Hulkenberg will keep Sebastian Vettel's seat at Aston Martin warm for the second weekend in succession as the four-time world champion continues to recover from his bout of Covid.
As a reminder, the Pirelli tyre compounds on offer this weekend are the C4 soft, C3 medium and C2 hard.
Alpine's Fernando Alonso led the field out onto the track when the light went green at the end of the pitlane, the Spaniard followed by a healthy contingent of cars.
As Verstappen set the first benchmark time, Haas ordered Kevin Magnussen to box as the team suspected a gearbox hydraulic issue. Unfortunately, the problem would deprive the Dane of the entire session.
Verstappen - shod with the hard rubber - continued to improve but 18 minutes into FP1, proceedings came to a red flag halt, a stoppage caused by McLaren's Lando Norris who, running close to a wall, destroyed a 50m marker board that had come loose at Turn 1, which required a proper clean-up.
The session resumed with 33 minutes to go and with Verstappen topping the time sheet with a 1m30.888s that led AlphaTauri pair of Yuki Tsunoda and Pierre Gasly, his teammate Sergio Perez and Mercedes' Lewis Hamilton who was 2.104s adrift.
The seven-time world champion did little during the session to alleviate the concerns of his team, noting that he was feeling "a lot of bouncing" onboard his W13 despite Jeddah very smooth track surface compared to Bahrain.
With a little over 20 minutes left on the clock, Bahrain GP winner Charles Leclerc jumped t second, 0.582s off Verstappen's best, but the Monegasque was overhauled in short order and pushed back to third by Gasly.
Despite running on the soft tyre, Verstappen failed to improve on his fastest lap, but that wasn't the case for Leclerc who shaved off several off his best time to push his Red Bull rival off the top and conclude FP1 at the top of the timesheet.
A late effort from Valtteri Bottas allowed the Alfa charger to snatch third, ahead of Sainz, Gasly and Tsunoda.
Further back, Perez, Esteban Ocon, Hamilton and Alonso rounded off the top ten.
Daniel Ricciardo was the fastest of the McLaren drivers in P11, while Norris was P13.
George Russell's opening session saw the Mercedes driver clock in a lowly 15th, just ahead of Aston Martin super-sub Nico Hulkenberg.
Williams' Alex Albon and Nicholas Latifi, and Haas' Mick Schumacher closed out field, with Magnussen lingering at the bottom after achieving just two exploratory laps in the 60-minute session.
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