Reigning MotoGP champion Marc Marquez led the way in first practice for this weekend's Dutch TT at Assen, beating Maverick Vinales by a little under two tenths of a second.
Marquez spent the early part of the 45-minute Friday morning session trading the fastest time with Pramac Ducati rider Danilo Petrucci, before Vinales took over at the top midway through.
The Yamaha rider set a 1m34.550s that stood as the benchmark until the final 15 minutes, when Honda man Marquez went top with a 1m34.411s.
Amid a flurry of improvements in the final few minutes, Marquez improved to a 1m34.227s, with Vinales falling 0.177s short with his best effort of 1m34.404s.
Valentino Rossi, whose most recent race victory came at Assen a year ago, made it two works Yamahas in the top three, just a tenth behind Vinales and 0.286s slower than Marquez's benchmark.
Jack Miller - who picked up his first and so far only MotoGP win at Assen in 2016 - was the quickest of the Ducati riders on his year-old Pramac machine in fourth place, a little under a tenth quicker than works rider Andrea Dovizioso.
Jorge Lorenzo suffered a late crash at the Turn 9 left-hander on the second of the factory GP18s, but was still able to set the seventh-fastest time behind lead Suzuki man Andrea Iannone.
Franco Morbidelli (Marc VDS Honda), Cal Crutchlow (LCR Honda) and Petrucci completed the top 10.
Dani Pedrosa was only 14th fastest on the second works Honda, 0.955s slower than teammate Marquez.
Bradley Smith survived an early trip through the gravel to lead the KTM charge in 16th, one place ahead of leading Aprilia rider Aleix Espargaro.