Fresh from his podium finish last time out at Donington Park, Jakub Smrz set the pace during first free practice for the third round of the 2011 World Superbike Championship at Assen.
The Czech rider produced his best towards the end of the session to vault an ever-changing leaderboard, Smrz emerging four hundredths faster than fellow Ducati man and series leader Carlos Checa.
Indeed, four riders occupied the top spot in the final five minutes, with Noriyuki Haga originally looking on course to hold firm aboard the PATA Aprilia after a series of fast laps mid-session enabled him to stay quickest up until the closing stages.
He would eventually be bumped down to fourth place behind the two Ducatis and Jonathan Rea, who was never outside the top five at any point in the session.
BMW recovered from a slow start to get both Troy Corser and Leon Haslam up to fifth and sixth, ahead of reigning champion Max Biaggi, while Eugene Laverty's late effort put him marginally ahead of Yamaha team-mate Marco Melandri in eighth and ninth. Ruben Xaus completed the top ten.
Another typically close session, just one second covered fourth down to 16th, with Leon Camier and Tom Sykes classified in 11th and 15th positions.
WSBK newcomer Barry Veneman, deputising for James Toseland at BMW Italia this weekend, made an encouraging start to briefly feature inside the top ten, before the Dutchman eventually slipped to 14th.
Elsewhere, Sylvain Guintoli, who is still suffering from injuries sustained at Phillip Island, was 17th, while Chris Vermeulen was out on track for just seven laps on the way to 19th.