UND (16-15), the third seed, plays second seed Weber State at 5:30 p.m. Friday in a BSC semifinal.
"I was pleased with our effort," SUU coach Nick Robinson said. "Our execution wasn't great in the second half. A tough loss is a tough way to go out."
SUU (11-20), which dropped its final eight conference games, was icy cold from the floor, shooting a lowly 29 percent. But the Thunderbirds hung around, trailing by three going into halftime.
A UND spurt to open the second half pushed the lead to 10, and the rout was on.
"In the first half, both teams were kind of tight," North Dakota coach Brian Jones said. "At the end of the first half, we found our rhythm defensively."
And offensively, too.
UND shrugged off its first-half woes and exploded for 41 points in the second 20 minutes. The team's backcourt duo of Aaron Anderson and Troy Huff was able to exploit a tired SUU defense for 29 combined points.
Meanwhile, the Thunderbirds needed points from their leading scorers and didn't get them. Jackson Stevenett, the BSC's second-leading scorer, finished with 15 points, but on 5-of-18 shooting.
Damon Heuir, the league's third most potent offensive threat, targeted by UND, was 1 of 10 from the floor. He finished with eight points.
Stevenett credited North Dakota's physical, team defense.
"When we got past someone, there was always someone else there stepping up," he said. "We came out with a lot of energy. In the second half we kind of let down a little bit, and that led to open 3s."
Storylines SUU loses quarterfinal
R Southern Utah could convert only 29 percent of its shots from the floor, 17 of 59.
• North Dakota blew open a close game with a flurry of 3-point baskets to open the second half.
• UND dominated the inside, outscoring the Thunderbirds 24-12 in the paint.