Valentino Rossi has scored one of his greatest MotoGP victories after a stunning bar-to-bar battle with Casey Stoner during Sunday's US Grand Prix, which ended in favour of the Italian when Stoner dropped his Ducati with eight laps to go.

Acutely aware of Stoner's awesome practice pace, which saw the Ducati rider lead every track session by at least 0.447secs, Rossi was determined not to let Stoner break away in the race - and made his intentions clear before the end of the first of 32 laps.

Stoner took the lead from pole but Rossi - who joked on Saturday that he needed a 30-second head start to beat Stoner, and that 'the only way to stop Stoner was to shoot him' - gave the young Australian a taste of what to expect by diving inside the Ducati rider on the entry to the corkscrew.

But the real action between the pair began on lap four, when Stoner retook the lead from Rossi into turn one, only for Rossi to fling his Fiat Yamaha back underneath into Turn Five.

Stoner was back ahead on the run up to the corkscrew, when Rossi again lunged inside - this time running over the dirt as he dived downhill, pushing both riders wide on the exit!

If Stoner had any doubts about how determined Rossi was to stay ahead of him, they were eradicated on the following lap when Stoner once again took the lead along the home straight - and again Rossi block passed him straight back into Turn Five.

Stoner's next assault came on lap 14, when he ran around the outside of Rossi through turn one - but outbraked himself into the double apex, forcing him to tip-toe back onto the racing line.

If Rossi had been trying to rattle Stoner, it looked to be working.

Nevertheless, Stoner still possessed the better ultimate pace and had re-caught Rossi within two laps. The deciding moment of the race then occurred when Stoner's rear wheel bobbled under braking for the final turn on lap 24.

The Australian came close to clipping Rossi before running wide and dropping his Desmosedici when the front wheel dug in to the deep gravel.

Stoner rejoined in a safe second position, while Rossi made a double-take at his pit board when it revealed his now untouchable lead the next lap around.

Rossi officially won his fourth race of the season, and first since Mugello on June 1, by 13.001secs from Stoner, and celebrated by kissing the asphalt at the top of the corkscrew. Rossi's previous best finish at Laguna Seca was third in 2005.

Rossi now leads the 2008 world championship by an enlarged 25 points from Stoner heading into the summer break, with the absent Dani Pedrosa dropping to third.

Stoner, who later criticised some of Rossi's moves, brought his Ducati home 13.608secs in front of third placed Chris Vermeulen.

Vermeulen had indicated his podium potential during free practice, but qualified just eighth on the grid. The Rizla Suzuki rider, third last Sunday in the German rain and something of a Laguna Seca specialist, was up to fifth by the end of the opening lap and eventually levered third place from home hero Nicky Hayden and JiR Honda rider Andrea Dovizioso.

Dovizioso did his hopes of securing Hayden's factory ride for 2009 no harm by taking fourth place from the Repsol Honda rider with eleven laps to go, then holding off the double US GP winner by less than one second at the line - making Dovi the highest placed Michelin rider.

Most Michelin riders had struggled badly with over-conservative tyres during practice, but some faired better than they had feared in the race - despite an all-Bridgestone podium - with Honda LCR's Randy de Puniet completing a Michelin fourth, fifth and sixth in the main event.

Alice's Toni Elias finished as the second best Ducati rider in seventh, but was capable of much more had he not dropped from sixth to tenth on lap six... and then back to twelfth place on lap eight.

Reigning double AMA Superbike champion Ben Spies finished his second MotoGP race in eighth position for Rizla Suzuki, a result he didn't seem too impressed with. James Toseland was also unhappy after slipping from fifth on the grid to ninth for Tech 3 Yamaha, while Shinya Nakano completed the top ten for Gresini Honda.

Kawasaki's replacement rider Jamie Hacking matched AMA rival Spies for much of the race before losing out to Elias and Nakano in the closing stages, costing him his target of a top ten finish by just one position.

Fellow American Colin Edwards rode with a special stars and stripes livery on his Tech 3 Yamaha for his home race, but it did him no favours as he sunk from seventh to 14th, ahead of an equally disappointed Loris Capirossi on the third GSV-R.

Stoner's team-mate Marco Melandri finished what might be his final Ducati race in 16th, after running off track on lap ten - a mistake that relegated the Italian from ninth to 17th and last, a position that eventually went to Kawasaki's Anthony West.

Only one rider failed to finish and that was Rossi's team-mate Jorge Lorenzo.

The MotoGP rookie, who has been trying to rebuild his confidence after some nasty accidents, lasted less than half a lap at his first US Grand Prix before a brutal highside - which equalled his Shanghai accident in terms of height - sent the Estoril winner bouncing through the gravel and nursing a foot injury.

While Lorenzo spends the summer break healing his latest wounds, Rossi will have three weeks to savour a truly memorable victory before the Czech Republic Grand Prix at Brno on August 17.

US Grand Prix:

1. Rossi
2. Stoner
3. Vermeulen
4. Dovizioso
5. Hayden
6. de Puniet
7. Elias
8. Spies
9. Toseland
10. Nakano
11. Hacking
12. Guintoli
13. de Angelis
14. Edwards
15. Capirossi
16. Melandri
17. West