Smolders completed a 12-pair jump-off in 40.92 seconds, just ahead of Olympic champion Steve Guerdat with Sydney, who stopped the clock at 41.55 seconds.
The Swiss had to settle for second, with Belgian Gregory Wathelet on Desteny completing the podium in third place.
Smolders won a car for his efforts, while Guerdat received 6,500 euros and Wathelet 4,900 euros.
Victory went some way to confirming that Smolders's nine-year-old Belgian horse has reached another level over recent months.
Already a winner of a Grand Prix on the Vilamoura Atlantic Tour in Portugal and a runner-up two weeks later, again in Vilamoura, Emerald then impressed in the Grand Prix at the 's-Hertogenbosch World Cup qualifier, when other riders, including Ludger Beerbaum, were forced to retire.
Emerald's talent over the fences has never been in doubt, but with Smolders this weekend he proved he has the pace to go with it. The issues of efficiency, particularly in turns, that had previously slowed him down now appear to have been ironed out.
And if he can translate his current form to the big fences of the CSI5*, Smolders may well have found himself a worthy successor to the likes of Regina Z and Exquis Walnut de Muze, the two leaders of his stables.