Red Bull's Max Verstappen set the pace in first practice at his home Dutch Grand Prix, ahead of Fernando Alonso and Lewis Hamilton.
The two-time world champion was 0.278 seconds ahead of Alonso, whose Aston Martin has an upgrade.
But it was not all plain sailing for the Dutchman - he went off into the gravel at Turn 11 right at the end of the session.
Hamilton's Mercedes was third quickest, with Red Bull's Sergio Perez fourth.
Verstappen is bidding for a record-equalling ninth consecutive win this weekend, which would match former Red Bull driver Sebastian Vettel's 2013 record.
The session was held on a dusty track - plumes of sand were thrown up by any car going off line - and Nico Hulkenberg suffered a crash when he lost control of his Haas through the penultimate corner and spun into the barriers, damaging the car's front wing.
Williams driver Alex Albon impressed with the fifth fastest time, ahead of McLaren's Lando Norris whose car has been the second fastest on average behind the Red Bull in qualifying since its upgrade at the Austrian Grand Prix early last month.
Their team-mates Logan Sargeant and Oscar Piastri were seventh and eighth, with the Alpha Tauri of Yuki Tsunoda and Alpine's Esteban Ocon completing the top 10.
Ferrari seemed to be struggling - Charles Leclerc was down in 16th, although he did not do a run on the fastest soft tyres.
Alonso was another driver to have an off. Like Verstappen, but earlier in the session, he entered the Turn 11/12 chicane too fast and ran across the gravel on the inside of the corner, to no apparent ill effect.
Aston Martin have a significant upgrade this weekend - a new floor design aimed at improving their performance after they slipped to the back of the four-team pack chasing Red Bull over the final part of the first half of the season.
Mercedes, for whom George Russell was 11th fastest, also have a floor upgrade, although more subtle than Aston Martin's. Hamilton was just 0.095secs behind Alonso as he looked to find early pace.
Zandvoort is already full of Dutch fans here to celebrate their hero, many decked out in orange T-shirts and generating a party atmosphere at this resort on the North Sea.