Charles Leclerc led a Ferrari one-two in Dutch Grand Prix second practice while Lewis Hamilton missed most of the session with an engine problem.
Hamilton’s Mercedes stopped on track after he had done just one flying lap. He was classified 11th.
Leclerc headed team-mate Carlos Sainz by 0.154 seconds.
Alpine’s Esteban Ocon was third, ahead of Mercedes’ Valtteri Bottas, Red Bull’s Max Verstappen and Alpine’s Fernando Alonso.
Seven-time champion Hamilton’s problem was the second engine issue for a Mercedes-engined car of the day, after Aston Martin’s Sebastian Vettel caused a 40-minute stoppage in the first session when he came to a halt at the exit of the pit lane.
The car remained by the side of the track where Hamilton had stopped, so he was unable to resume the session.
Mercedes said there was no indication the two power-unit problems were related or that they were circuit-specific.
Vettel’s was an engine failure which will be investigated back at Mercedes’ UK engine base after the race. Hamilton was asked to stop on track after the power-unit developed a problem.
Verstappen’s true competitiveness over one lap was hidden because there were two red flags during the session, one for Hamilton and another when Haas driver Nikita Mazepin spun off at the chicane, and both happened when the Dutchman was on a flying lap.
“It’s insane,” Verstappen said over the radio after the Mazepin incident. “I just can’t get a lap in, man.”
In total, about 15 minutes’ worth of running were lost from the session to the two incidents.
It meant Verstappen’s fastest time – just over 0.3secs off the pace – was set on tyres that were already past their best.
But the Red Bull driver looked blisteringly fast on the race-simulation runs later in the session when drivers use full fuel loads.
Verstappen was serenaded by an arena packed with Dutch fans vocalising their support for him on the return to the Zandvoort track to the F1 calendar for the first time since 1985.
Verstappen said: “It was really enjoyable to see all of them in orange and having fun in the grandstand and of course the track as well. It’s quite a short lap but a lot of fast corners. It was quite a fun day.
“In the short run, it doesn’t look very representative from our side, because already after one lap the tyres do drop off a bit. But nevertheless we will work on a few things where we are not entirely happy on the short run.
“But on the long we looked competitive. That is always very important but we also know the starting position is also very important so we will have a look at what we can do on the short run to make it better.”
Hamilton said: “I just lost power and they told me to stop. It is not the end of the world. It has been a beautiful day in terms of weather. It’s amazing to see the crowd. There are so many people here and it’s good to see people hyped. It’s the first time we’ve seen all the energy the Dutch fans bring.
“I only got 20 minutes of running this morning with the red flag so it naturally puts us on the back foot but Valtteri looked like he had a good session and hopefully tomorrow we can try and pick up some of the time.
“The track is epic. It’s really fantastic. It brought back so many memories. It’s crazy in an F1 car.
“But I don’t think we’ll be able to overtake. high downforce, super-fast corners we probably won’t be able to follow through.”
He was comfortably quicker than Bottas with both drivers on the soft tyre, but direct comparisons are not available because it is not known what engine modes the two cars were in.
Ocon and Alpine looked impressive all day, with the Frenchman quick on both short runs and long. Team-mate Alonso was just over 0.2secs behind.
Alpha Tauri’s Pierre Gasly, McLaren’s Lando Norris, Alfa Romeo’s Antonio Giovinazzi and Vettel rounded out the top 10.
Alfa’s Kimi Raikkonen, who announced on Wednesday that he would retire from F1 at the end of the season, was 16th fastest and Williams driver George Russell 20th and last.