Dani Pedrosa got the better of MotoGP title leader Jorge Lorenzo to lead opening practice for the US MotoGP at Laguna Seca on Friday morning.
The Repsol Honda rider, who has one of the early 2013 RC213V machines available for this weekend, got within a fraction of the race lap record with a best time of 1m 21.424s on his 19th of 20 laps.
Lorenzo - on pole for the US GP at Laguna Seca for the last three years and winner during his 2010 title season - had broken Pedrosa's dominance from the 31st to 41st minutes, but eventually finished just 0.074s behind his fellow Spaniard.
Pedrosa, winner at Laguna Seca in 2009, trails Yamaha star Lorenzo by 19-points in the championship standings.
Pedrosa's team-mate and reigning champion Casey Stoner, who has requested the new engine in the present chassis to try this weekend, was third quickest at the conclusion of the 45-minutes.
The defending US GP winner, who has slipped 37 points from Lorenzo after incidents in the last two races, lapped 0.405s from the top.
Lorenzo's team-mate Ben Spies, riding for the first time since announcing his end-of-2012 Yamaha exit, clamed top American honours in fourth (+0.515s).
Fifth place Andrea Dovizioso led the satellite challenge for Yamaha Tech 3, albeit a sizeable (for the shortest circuit on the calendar) 1.1s from Pedrosa. Team-mate Cal Crutchlow collected sixth (+1.248s)
Ducati are expected to debut 'some' new parts during this weekend, which began with Valentino Rossi seventh in FP1 and 1.7s from Pedrosa.
Team-mate Nicky Hayden, whose 2013 contract extension was announced just minutes before practice began, was ninth (+1.9s) with Honda LCR rookie Stefan Bradl splitting the factory GP12s.