Allied Racing's Bastian Buus was fastest in a trouble-free opening practice session at the Zandvoort circuit in the Netherlands.
Buus, driving the #22 Porsche, set the fastest time on his final lap, as conditions improved rapidly in the last 10 minutes of the opening practice session at the 4.2 km circuit.
The #15 NM Racing Team Mercedes-AMG was second fastest in the end and was one of the frontrunners in the opening practice session. Xavier Lloveras set the fastest time for the Spanish team.
Third and fourth overall were the two V8 Racing Chevrolets, with Jorge Cabezas beating teammate Thijmen Nabuurs by just 0.049s in the first practice session of the weekend.
French drivers Gael Castelli (#8 CMR Toyota) and Valentin Hasse-Clot (#27 AGS Events Aston Martin) completed the overall top six, with Jörg Viebahn taking second in Pro-Am in seventh overall.
Championship leaders Bas Schouten and Gabriele Piana ended the session in ninth place, 0.050s behind teammates Koen Bogaerts and Mark van der Aa, but 0.054s ahead of the CMR Toyota of Antoine Potty and Timothé Buret. Fastest in the Am class was the #31 SRT Mercedes-AMG of Bob Herber.
Other than a full course yellow for the recovery of one of the Aston Martins from the gravel trap at turn 8, there were no incidents during the opening session. All 18 cars will return to action later this afternoon for the second practice session.
FREE PRACTICE 1 RESULTS