The 38-year-old Rossi finished with a time of 41:41.149, averaging 169.9 kph, reports Efe.
Octo Pramac Racing's Danilo Petrucci of Italy took second place and Repsol Honda's Marc Marquez of Spain, finished in third place.
Rossi, who got his first win of 2017 at the TT Circuit here, is now in third place in the standings with 108 points.
Italian Ducati Team rider Andrea Dovizioso, winner of the two MotoGP races, is now in first place with 115 points, while Movistar Yamaha's Maverick Vi?ales of Spain is in second place with 111 points.
Rossi managed the race masterfully, edging Petrucci and Marquez for the win.
Tire selection proved to the the key to victory for Rossi, who decided to go with an intermediate composite in front and a hard tire in the back to deal with the weather conditions here.
The white flag came out with just eight laps left as rain began to affect the area around the track.
Vi?ales, who was the leader in the standings heading into Assen, had problems in qualifying and started 11th in the Dutch TT.
The Spanish rider moved ahead after the start of the race and was in 8th place by the seventh lap.
Vi?ales, however, was unable to break into the front and finish in the top three.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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