Robinson again showed his supreme skill despite having never raced a 250cc machine in the wet before! The Englishman made the best use of his second row starting spot and had climbed to fifth place by the end of the first lap. The QUB Team OPTIMUM Aprilia was working well in the wet and Robinson fended off the far more experienced Matsudo for many laps.
Daijiro Katoh was a lacklustre eighth, almost exactly a minute behind Ukawa at the flag. The Honda Gresini rider gave too much respect to Assen and its tricky surface. The changing conditions also meant that he erred on the side of caution whereas riders who have visited the track before were able to push harder, knowing what the surface was like.
Rounding out the top ten were Roberto Rolfo, guesting on Tino Vila's Honda and Vincent Philippe in what was his best result of the year so far.
Other than Robinson, British success was fairly thin on the ground with Vincent ruing his wrong tyre choice, sliding home a lap down in 19th and Adrian Coates retiring twelve laps from home.
Youichi Ui took a dominant flag to flag victory at Assen on Saturday for his third win of the season while Noboru Ueda snatched second two corners from home.
Japan's Youichi Ui took Derbi's first win at Assen since 1988 with a crushing flag to flag victory in highly treacherous conditions at the Dutch TT. Ui led away from pole position and was never headed once during the 17 lap race.
Manuel Poggiali provided the main opposition to Ui, the San Marino native charging from 24th on the grid to 4th on the opening lap and then proceeding to chase Ui for all he was worth. Gradually though, the 17 year old fell back and was eventually passed by a flying Noboru Ueda for second just two corners from home.
Ueda had been in inspired form after making a poor start from second on the grid. However he carved his way through the chasing pack, passing Emilio Alzamora, Steve Jenkner, Simone Sanna, Roberto Locatelli and Lucio Cecchinello before setting off after Poggiali.
Cecchinello eventually finished fourth, after starting 24th while Sanna came home fifth after holding down third in the early stages.
Alzamora was one of many riders to get caught out by the slippery conditions and retired on the penultimate lap when a points finish was out of the question. Others who fell included Randy De Puniet who had ridden a superb race up to third place before he lost it and was forced to retire. The right hander where De Puniet fell also claimed Kenny Roberts, Alzamora, William De Angelis, Franco Battaini and Toni Elias during the course of the meeting.