The Dutchman, atop his Olympic horse Sterrehof’s Tamino, bested Sweden's Malin Baryard-Johnsson with H&M Tornesch and Britain's Peter Charles with Murka's Odie de Frevent to take the honours at Olympia.
Charles was one of three Brits to qualify for the play-off, along with Nick Skelton and Guy Williams, to the delight of the home crowd, while strong competition also came from Olympic silver medallist Gerco Schroeder of the Netherlands.
But it came down to a three-way battle between Houtzager, Baryard-Johnsson and Charles, with the Brit setting the early pace with a safe round of 37:54 before Baryard-Johnsson bettered that time by nearly a second.
Houtzager trumped them all with a 34:67 to claim victory and win a crucial 20 points towards qualification for the World Cup finals in April.
Roger-Yves Bost 10th-place finish with Myrtille Paulois Castle Forbes boosted the Frenchman's points total to 39 points, almost guaranteeing him a place at the finals in Gothenburg.