Francesco Bagnaia headed the Moto2 timesheets on the opening day of practice ahead of the Dutch TT, with fellow MotoGP-bound rider Joan Mir a tenth behind in second.
Points leader Bagnaia set the pace in the opening 45-minute session for the intermediate class at Assen, a late 1:38.219s putting the Sky VR46 rider top of the pile.
Catalunya race winner Fabio Quartararo set the early pace in FP1 at a 1:39.262m, though was soon deposed by Bagnaia, who edged ahead with a 1:39.246s.
Times tumbled as FP1 came to a close, with Bagnaia's 1:38.219s putting him two tenths clear of surprise second-place man Andrea Locatelli on the lead Italtrans Kalex.
Quartararo was a tenth further back in third, while Brad Binder headed Lorenzo Baldassarri and Alex Marquez – who crashed early in the session – rounding out the top six in FP1.
Intact GP's Marcel Schrotter led the way in the opening stages of the second session, though his 1:38.526s was sharply usurped by Quartararo on the Speed Up bike with a 1:38.423s.
Mir took over from the Frenchman with a 1:38.191s on his Marc VDS machine, before Bagnaia returned himself to the top of the timesheets with a 1:38.091s.
Status quo remained amongst the leading two through to the chequered flag, with Luca Marini completing the top three on the sister VR46 bike.
Quartararo was shuffled back to fourth in the end from Baldassarri, while Mattia Pasini shot up to sixth on his Italtrans bike.
Marquez was half a second off the pace in seventh in FP2, though was eighth on the combined times as Locatelli's – who was 12th in the second session – 1:38.413s from FP1 kept him in seventh overall.
Early pacesetter Schrotter ended up ninth overall at the end of FP2, with Romano Fenati rounding out the top 10 ahead of Miguel Oliveira – who trails Bagnaia by a single point in the standings – and Sam Lowes.
Augusto Fernandez will remain at the Pons team for the rest of the 2018 season as the ousted Hector Barbera's replacement, and ended the day 15th.
A heavy fall at Turn 15 late on in FP2 saw Honda Team Asia rider Tetsuta Nagashima helped off track by medical staff, while Stefan Manzi walked away unscathed from a fast fall at Turn 1 moments later.
