WFR Honda's Alex Lowes was knocked off the top of the FP1 timesheets at Thruxton
following a late charge by Shane Byrne on the Rapid Solicitors Kawasaki.
Byrne was the only rider to break into the 1m15s bracket as he ended the opening session on top with a time of 1m 15.969s, with Lowes also overhauled by MCE British Superbike Championship veteran Chris Walker on the Pr1mo Bournemouth Kawasaki.
Paul Bird Motorsport rider Byrne's fastest lap of 111.64mph put him 0.335s ahead of Walker, while Lowes' WFR team-mate, James Westmoreland, slotted into fourth.
Current champion Tommy Hill, who failed to score any points in the opening round of the series after crashing out in the wet at Brands Hatch, powered his way into fifth position on the Swan Yamaha YZF-R1.
Hill was 0.928s was adrift of Byrne, but completed fewer laps than anyone on track in FP1, with just 11 laps on the 1000cc Yamaha enough to put him ahead of Ulsterman Ian Lowry.
The Padgetts Honda rider made a superb debut at Brands for Clive Padgett's team as he finished in fourth position and has made a positive start at Thruxton.
Lowry had been holding second place on the timesheets for much of the session before he dropped down the order on the CBR1000RR.
Dan Linfoot was next on the Buildbase BMW S1000RR with a time of 1m17.058s keeping him ahead of leading Tyco TAS Suzuki rider Josh Brookes, with Michael Laverty on the Samsung Honda in ninth (1m17.405s), 1.436s behind Byrne.
Graeme Gowland rounded out the top ten on the WFR Honda to join his team-mates Lowes and Westmoreland in the top half of the leaderboard.