Valtteri Bottas led Max Verstappen during a wet-dry opening practice for the Belgian Grand Prix, with Lewis Hamilton down in 18th, as the F1 field returned to action after the month-long summer break.
Friday's first session at Spa-Francorchamps began in damp conditions, with drivers initially venturing out on the Intermediate tyres. Just under 15 minutes into the hour, McLaren's Lando Norris led the switch to slicks, with lap times and improvements flowing thereafter.
Bottas ultimately came out on top with a time of 1:45.199 on the Soft tyre, Pirelli having brought the three medium tyres in their range to Spa – the white-marked C2, yellow-marked C3 and red-marked C4.
Verstappen threatened to steal top spot late on, amid a series of improvements on Softs, before further raindrops fell. He wound up 0.164s behind Bottas, as Red Bull and Mercedes prepare to continue their battle for the 2021 world titles.
Hamilton, running a larger rear wing than teammate Bottas in FP1, which he described as "massively slow on the straights", finished 18th after a tricky session.
It almost ended in disaster for the championship leader when he caught Nicholas Latifi on the run down to the Bus Stop chicane and narrowly avoided a collision – the Williams driver, holding the racing line, seemingly unaware of the approaching Mercedes man on his outside. Hamilton darted to his left to prevent contact and backed out of his lap.
Hamilton therefore lacked a representative time on the softest rubber, leaving him over three seconds off the pace.
Result Free practice 1 - Belgian
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Pierre Gasly took advantage of the changeable conditions to put his AlphaTauri third on the timesheets, ahead of Ferrari pair Charles Leclerc and Carlos Sainz. As the session wore on, Leclerc was lucky to avoid the barriers after running wide at Malmedy and taking a trip through the gravel trap.
Sergio Perez again trailed teammate Verstappen by a significant margin in sixth, with Aston Martin's Sebastian Vettel, the aforementioned Norris and the Alpines of Esteban Ocon and Fernando Alonso rounding out the top 10.
There were incidents further down the order as Kimi Raikkonen and Yuki Tsunoda both spun out of La Source in the drying conditions, Tsunoda almost reversing into Perez, who was leaving the pit lane, as he recovered his car.
Raikkonen had another moment later in the session as he clipped the inside wall on the entry to the pits, leading to a sweary message over the team radio, but the Finn was able to continue.
Video: The secrets of the Spa-Francorchamps F1 circuit
Follow Rudy van Buren as he takes you on a flying lap around Spa-Francorchamps while explaining what makes the track so exciting.