Valtteri Bottas put behind him his uncertain future with Mercedes to take first practice honours ahead of the Belgian Grand Prix on F1's return to action.
After the traditional summer break, Bottas made the most of the dry running early in a weekend in which rain is predominantly forecast to post a leading time of one minute 45.199secs.
The Finn, who is vying for his future at Mercedes alongside Williams' George Russell and who will serve a five-place grid penalty for causing the first-corner collision in the last race in Hungary, finished 0.164s clear of Red Bull's Max Verstappen.
As for Verstappen's title rival Lewis Hamilton, the seven-time champion finished in a lowly 18th place but that was due to an anxious moment in the final sector on his hot lap with Nicholas Latifi in his Williams.
Hamilton was just over a tenth of a second quicker after the first two sectors at the Spa-Francorchamps circuit when he attempted to overtake Latifi around the outside on the approach to the final chicane.
Latifi appeared to be clearly unaware Hamilton was to his left, forcing the Briton to brake sharply to avoid a collision, leaving the Briton with a time that left him three seconds off the pace of his team-mate.
The session was an intriguing one as the two W12s ran different rear wings as the team explored contrasting downforce levels around a circuit that is difficult to master given the long straights in the first and third sectors but possesses numerous corners in sector two.
Hamilton's car was running higher downforce compared to the lower setting for Bottas due to a much skinnier wing on the Finn's car, with the latter better in dry conditions and the former required for wet running.
The duo were also among a number deploying new power unit elements, notably an internal combustion engine, turbocharger, MGU-H and MGU-K, providing the cars with an advantage for a high-power circuit.
Due to the conditions, the early running saw a number of drivers conduct what is fair to describe as 'tiptoe' laps around the circuit on intermediate tyres.
Rain had fallen in the build-up to the opening hour-long session, yet despite the cold temperatures of just 12 degrees centigrade at the start, the surface had dried to a certain extent.
The majority of the field, however, took to the longest track on the calendar at seven kilometres on the green-striped intermediates but only for a lap as it quickly became apparent slick rubber was required, providing dry running for the rest of the session.
Leclerc had an anxious moment of his own when he ran onto the new gravel trap at turn seven, forcing him to fight for control of his car to avoid a collision with a barrier.
Sergio Perez, also running new power unit elements after his second system was lost as he was one of the first-corner victims in Hungary, was sixth quickest, nearly a second down, followed closely by Aston Martin's Sebastian Vettel.
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7 - 9 Jun
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21 - 23 Jun
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28 - 30 Jun
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5 - 7 Jul
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19 - 21 Jul
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26 - 28 Jul
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23 - 25 Aug
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13 - 15 Sep
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18 - 20 Oct
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25 - 27 Oct
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1 - 3 Nov
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29 Nov - 1 Dec
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6 - 8 Dec
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