Reigning six time MotoGP world champion and 2009 title leader Valentino Rossi set the fastest time in Friday practice for the US Grand Prix at Laguna Seca on his 32nd and final lap of the Californian circuit.

Rossi, who won an epic duel with Casey Stoner at Laguna Seca last season, had led the one-hour session early on - but it was Stoner who spent most time on top.

The Ducati star had been over half a second ahead at one point, but was then steadily reeled in by both Rossi and Fiat Yamaha team-mate Jorge Lorenzo. Lorenzo took the top spot from Stoner with just over ten minutes to go and the three title contenders were covered by just 0.077sec as the final minutes began.

Rossi regained second position from Stoner on his penultimate lap, then brushed 0.112sec under Lorenzo's best on his final lap. Fresh from his third victory of the season, and the 100th of his career, Rossi will start round eight with a five point lead over Lorenzo and nine point advantage over Stoner.

Lorenzo confirmed the M1 one-two by finishing 0.077sec ahead of Stoner, who has struggled with a mystery sickness at the last two rounds and looked off colour once again this afternoon, perhaps contributing to his late demotion.

With the top three in a class of their own, almost half a second separated Stoner from fourth placed Dani Pedrosa (Repsol Honda), who was followed on the timesheets by fellow factory RCV riders Toni Elias (Gresini Honda) and Andrea Dovizioso (Repsol Honda).

Marco Melandri, third at the 2007 US GP, was an impressive seventh on the Hayate-run Kawasaki, but 1.159sec behind countryman Rossi. Eighth place went to double Laguna podium finisher Chris Vermeulen, despite an early front-end fall from his Rizla Suzuki at the Turn Two hairpin.

Monster Yamaha Tech 3's Colin Edwards was the top American on day one, but ninth and 1.3sec behind Rossi is not what he would have wanted, while Alex de Angelis made it two Gresini riders in the top ten.

Randy de Puniet, who claimed his best result of 2008 with sixth at Laguna Seca, was eleventh in practice, closely followed by Loris Capirossi (Rizla Suzuki) and James Toseland (Tech 3 Yamaha). Toseland ran top ten for the first half of the session, then lost ground.