Rapid Solicitors Kawasaki rider Shane Byrne powered to the top of the time sheets during the opening practice session at Assen on his return from injury.
Byrne was the only rider to post a lap of the legendary circuit in the 1m 38s bracket, with his time of 1m 38.651s putting him clear of WFR Honda man Alex Lowes (1m 39.133s) and fellow Showdown contender Josh Brookes on the Tyco Suzuki, who lapped in 1m 39.200s.
Double BSB champion Byrne - who was sidelined at Donington after dislocating his collarbone - was in the mix throughout FP1 but posted his best time on his final lap to send Lowes into second position by less than half a second.
Luca Scassa on Clive Padgett's Honda saved his best until last as he edged into fourth ahead of Swan Yamaha duo Tommy Hill and the injured Noriyuki Haga.
In seventh position was Tommy Bridewell on the Supersonic BMW, narrowly ahead of new Splitlath Redmond recruit and ex-World Superbike star Jakub Smrz, who lapped in a time of 1m 39.949s on the Aprilia RSV4 on his debut for the team.
Ian Lowry and Jon Kirkham completed the top ten, although Kirkham's Samsung Honda team-mate – Michael Laverty – has work to do after ending FP1 in 13th position, one place ahead of Robbin Harms and behind Barry Burrell and Stuart Easton in 11th and 12th places respectively.
Alastair Seeley continues to struggle to make progress on the Tyco Suzuki, with last year's British Supersport champion languishing in 24th.
MSS Bathams Kawasaki rider Michael Rutter was down in 28th. His team-mate, Danny Buchan – who sustained a fractured collarbone in a crash at Cadwell Park – did not compete in the session.
to view FP3 times