The Pilots hosted the No. 22 Bulldogs on Thursday night and led from the start en route to an 82-73 victory.
The win snapped a 20-game losing streak to the defending West Coast Conference champion Zags. The perennial NCAA tournament darlings had won 22 straight conference games dating back three seasons.
Van der Mars was caught up in the postgame celebration when the purple-clad Pilots fans stormed the court. He had never seen anything like it.
"Only on ESPN," he joked. "And I've seen some footage of our win against St. Mary's the year before I got here. But it was nothing like this."
Before bursting into happy laughter, he said: "Obviously, it's a great feeling."
Van der Mars has had a breakout year this season for the Pilots (10-7, 2-3), averaging career highs with 12.8 points and 6.8 rebounds. When he had 19 points and 18 rebounds against Portland State on Dec. 7, he became the first Pilot since 2011 to earn West Coast Conference player of the week honors.
After going 20-10 overall in 2011, the Pilots have struggled and last season they finished 11-21. With the victory over Gonzaga, they're a win away from last season's total.
The last time the Pilots beat the Bulldogs in Portland was in 1996 and the Pilots' last victory in the series came in 2003 in Spokane. Portland had not defeated an AP-ranked opponent since 2009 when the Pilots beat then-No. 22 Minnesota.
Portland led by as many as 17 points in the second half. The win was more about Portland's eagerness than Gonzaga's lack of it.
"It feels pretty good. When I first came into the league, (San Diego coach) Bill Grier used to joke, 'You'll become a Zags hater.' And I don't hate the Zags at all. They're so great for the league, they're so great for us, and Coach (Mark) Few is a great coach and a fierce competitor," Pilots coach Eric Reveno said. "I've always said, I don't want them to get any worse, I want us to get better."
Sophomore guard Bryce Pressley had 16 points and a career-high nine assists to lead the Pilots. Freshman guard Alec Wintering added 14 points and four assists even though his legs cramped up in the second half and he had to head to the locker room for an IV.
Van der Mars finished with 11 points and five rebounds.
The Zags cut the deficit to 39-35 early in the second half, but van der Mars and Wintering hit consecutive jumpers - and van der Mars added another for good measure - and Gonzaga couldn't get closer than nine points the rest of the way.
"They played with way more energy and way more passion," Few said afterward. "Portland did a good job of bringing it tonight."
Van der Mars, who is from Gouda, Netherlands, played for the Dutch U-20 national team and trained at the Canarias Basketball Academy in Spain before coming to Portland. He said it was by far the biggest win of his career.
"We build the lead from the ground up, and we made great winning basketball plays consistently," van der Mars said. "It wasn't up and down basketball. It was a very consistent effort."
Teammate Ryan Nicholas agreed that it was a defining victory.
"That's what you work for, those kinds of moments," he said. "We seniors, we've been grinding it out for four years every summer, and this last summer, all of us, together, worked very hard. Every morning, get up, work out, even when this game wasn't in view, and it was all for this moment."