The CAS Honda rider dominated race one, but was forced to settle for second behind fellow Belgian Steve Ramon in the final race of the day, in which KTM David Philippaerts was third. However, with Ramon finishing just fifth in race one, de Dycker could safely allow the Suzuki star to pass without threatening his overall victory.
"It still really needs to sink in that I have won," said Ken. "It was all about the starts and I got away well in the first moto and had some good lines. It was a smooth ride and I did not make too many mistakes. The track was really bumpy and different for the second moto. I was doing OK at the beginning but there were a few mistakes and I was happy to take second as it still meant I had the GP. I had some problems at the beginning of the season and also a little injury but things are getting better for me now."
de Dycker and Ramon were joined on the podium by Kawasaki's Tanel Leok, who took second place in race one but only managed fifth in the second moto, behind team-mate Billy Mackenzie. Ramon's team-mate Kevin Strijbos had stunned with pole on his return from injury - and finished third in race one, but limped home outside of the points in race two.
Meanwhile, runaway world championship leader Josh Coppins experienced his toughest event of the season so far, finishing fourth and sixth.
"It's been a bad weekend for me," admitted the Yamaha star, who suffered a bout of flu coming into the event. "I had no physical power and never felt good all weekend - I just struggled. The other guys were all really fast and were attacking and I couldn't retaliate. I didn't get good starts in any of the moto's which didn't help out all. I have managed to limit the amount of points lost and still have a comfortable lead but am disappointed with today."
Coppins still holds the championship red plate with an 89 point advantage over Ramon heading into the 10th round at Faenza, Italy in two weeks time.
Meanwhile, in the MX2 class dominant world championship leader Antonio Cairoli suffered a scare when he crashed with Tyla Rattray at the start of race one, but the Italian was able to storm all the way back to second behind debut moto winner Tommy Searle, Rattray's young factory KTM team-mate. Tyla himself retired with a knee injury, while world champion Christophe Pourcel was fifteenth after a fall.
Race two saw Cairoli take a dominant victory, and with it the overall, while Pourcel claimed second despite another fall. A brave Rattray rode to a sore third while team-mate Searle could manage no better than fifth after a slow start - but still secured second overall, ahead of fellow KTM rider Marcus Schiffer, whose 7-6 results gave him a surprise podium.
In the championship standings, Cairoli is now an increased 102 points clear of Pourcel.
In the FIM Women's Motocross Cup, defending champion Katherine Prumm of Kawasaki Molson was back on top, after a disappointing opening round in Teutschenthal, thanks to 3-1 moto finishes, although Livia Lancelot was only one point behind after two solid second places.
Lancelot is the new series leader, taking the red plate after previous leader Larissa Papenmeier claimed only fourth overall.
Maria Franke completed the podium, but drops down to third in the series, behind Lancelot and Prumm, with the latter moving up from fourth to second.