Netherlands international center Van Paassen poured in 24 points and hauled in seven rebounds as the Dutch team improved to 4-2 to clinch second place in Group L behind BC Triumph and advance to the Quarter-Finals.
Chris Finch's Dexia, which lost both of its games to EclipseJet MyGuide, dropped to 3-3.
Tuesday's game between the Amsterdam outfit and Dexia was close from start to finish.
Tamien Trent's lay-up gave the visitors a 77-75 lead midway through the final quarter, only for Great Britain international Nate Reinking (19 pts) to answer with a jump shot to level the game soon after.
The Dutch outfit then landed some blows that Dexia ultimately did not recover from.
Teddy Gipson buried a jump shot, Orien Greene hit a three-pointer and Victor Thomas dunked as Arie Shivek's team took an 84-77 lead with 3:02 to go and forced Finch to call a timeout.
Dexia, beaten finalists in last year's EuroCup, clawed their way to 87-86 on Caleb Green's three-point play with 33 seconds remaining and Amsterdam's Israeli coach Shivek decided to burn a timeout.
When play resumed, Clint Harrison came up with two big plays for the Dutch team.
First, he received a pass from Gipson and drained a jump shot for a three-point advantage. Harrison then came up with his third steal of the game when taking the ball away from Reinking.
Van Paassen and Harrison each made two free throws to finish the scoring, and end the EuroChallenge campaign for a disappointed Dexia.
Greene and Harrison each had 19 points for the winners, who were 12 of 25 from three-point range.
Harrison made four of five behind the arc and both Greene and Gipson hit three treys.
Trent was also lethal, burying two of his four attempts.
Dexia's Green finished with 18 points
The home side struggled at the free throw line, making 18 of 28.
They were 10 of 23 from three-point land.
Arie Shivek (coach of EclipseJet MyGuide Amsterdam):
"Just before the game, I told my guys that the the players of Dexia wera able to run away [with the score], and then we had to keep our cool, because Nesbitt, Reinking, or Conlan were able to make the difference in a few minutes. It wasn't top secret to know that Dexia had the best rebounders of Belgium, and also the team was very strong in the defensive transition, but after we succeeded to go ahead, I was confident in the management of the last minutes. Now, against Proteas it will be two tough games because maybe we'll play two times in Cyprus, but I'm sure that my guys are not afraid of playing away because in the second round, we won in Samara and Mons, and we were beaten at the buzzer in Moscow."
Orien Green (player of EclipseJet MyGuide Amsterdam):
"The coach had told us before the game that it would be very difficult to win here except if we remained concentrated from the beginning to the end. And that is what happened, because we played aggressive defense, and also very hard. I think we deserved our success as we didn't yield to the circumstances at the times when Dexia was ahead. It's a good thing to be in the Quarter-Finals, this will strengthen the team for the future."
Travis Conlan (player of Dexia Mons Hainaut):
"Certainly some players didn't play at their [best] level, but it's also certain that the Dutch team was very strong, and also difficult to move in defense. In fact, they made the difference with some big shots at the critical moments, and that way of playing prevented us to develop our game as we're able to do. Moreover, in the fight for the rebounds, we had some problems and in the last quarter, we paid for those failures."