Click here for full World Superbike FP1 results from Laguna Seca
Alex Lowes has nipped ahead of Chaz Davies in a qualifying-style blast after FP1 was restarted for a final three minutes following a red flag suspension due to oil on the track.
Last year's double winner around Laguna Seca Davies had set the pace having headed the times for the majority of the opening practice session, with his best time of 1m 23.971s giving him a third of a second advantage of his nearest rivals Lowes and Michael van der Mark.
But FP1 was suspended with just over three minutes remaining after Peter Sebestyen suffered a nasty fall at turn 11 that saw oil split on to the circuit which required a clear up.
After a 12-minute delay the action resumed which enabled Lowes a quick-fire blast to take top spot from Davies by 0.059s, while World Superbike championship leader Jonathan Rea nipped into third with less than one-tenth covering the top three.
With van der Mark edged into fourth he headed Honda team-mate Nicky Hayden, while Xavi Fores on the Barni Ducati also produced a late improvement to leapfrog into sixth.
Sylvain Guintoli stand-in Niccolo Canepa placed his Pata Yamaha seventh overall as Jordi Torres, Davide Giugliano and Tom Sykes completed the top ten runners.
Leon Camier was an absentee on the MV Agusta RC F4 RR after the British rider failed to set a single lap in the entire session due to a technical problem.