Rossi snatched victory 1.909-seconds ahead of championship leader Casey Stoner of Australia with American reigning champion Nicky Hayden third at 6.077 after 26 laps on the TT track.

It was a remarkable victory for Rossi who started 11th on the grid but had already risen to third with a quarter of the race run.

Stoner quickly passed pole-sitter and countryman Chris Vermeulen and he was soon followed by American John Hopkins.

Hopkins failed to exert much pressure on Stoner but that came soon enough as a storming Rossi passed the American just before the halfway mark in the race.

The battle for victory raged with Rossi hounding Stoner until three laps from the end when he passed the 22-year-old on a long corner and comfortably eased away to reignite his championship bid.

"It's a great result. I didn't really expect to have such an achievement," said Rossi.

It was the sixth win at Assen for Rossi, having won four times in MotoGP, 2007, 2005, 2004, 2002, once in 250cc in 1998 and once in 125cc in 1997.

Stoner now leads Rossi by just 19 points at the top of the standings.

But Rossi's confidence is building at the half-way stage of the 18-leg world championship series.

"It's not a slim margin by any means against a rider of Casey's calibre. But if we succeed in improving the motorcycle and above all the tyres, everything remains possible."

Rossi has room to work on the improvements he needs as the next round takes place in Sachenring, Germany on July 17.

In the 250cc category, world champion Jorge Lorenzo of Spain achieved his sixth and perhaps easiest win of the season.

The Aprilia rider consolidated his championship lead by finishing comfortably ahead of San Marino's Alex De Angelis and Spaniard Alvaro Bautista.

Italian Mattia Pasini of Aprilia lead from start to finish to win the 125cc category, six days after winning his first race at Donington.

Second place was enough for Spaniard Hector Faubel of Aprilia to extend his world championship lead.