Jonathan Rea ended day one at Assen fourth fastest after being knocked off the top spot in the third free practice session.
The Kawasaki rider had topped the times in FP1 and FP2 on Friday before home favourite Michael van der Mark shot to the top on the PATA Yamaha, setting the fastest time in 1m 35.156s.
Van der Mark was 0.243s ahead of Aruba.it Ducati’s Marco Melandri in second, with Michael Ruben Rinaldi – competing in only his second World Superbike round – third quickest for the Aruba.it Ducati Junior team.
Ulsterman Rea, who completed more laps than anyone on his Ninja ZX-10RR, was unable to improve on his best time from FP2 as he slotted into fourth, 0.474s behind van der Mark.
His team-mate Tom Sykes, who had been second in FP2, finished the day in sixth behind Alex Lowes (PATA Yamaha).
Spain’s Xavi Fores (Barni Racing Ducati), who was leading race two last weekend at Aragon before he slid off, finished seventh ahead of Wales’ Chaz Davies (Aruba.it Ducati), who trails Rea by 12 points in the world standings after the first three rounds.
Three-time champion Rea has won the last seven races at Assen, including six-in-a-row for Kawasaki.
In the World Supersport Championship, Andrew Irwin was 22nd fastest on the CIA Landlord Insurance Honda.
Final practice and Superpole qualifying takes place on Saturday ahead of WSBK race one, which is scheduled for 12:00 BST.