Denver led 38-32 at halftime, then held South Dakota to 23 second-half points on 35 percent shooting. Olson's 3-pointer to start the second half gave Denver a nine-point lead.
Bryant Rucker had 14 points for Denver (16-14) and Jalen Love added 12. The Pioneers forced 11 turnovers, leading to 20 points.
The Coyotes trailed 60-50 with 3:46 left, then only made one more field goal, a Tavian Pomlee 3-pointer with 40 second left, the rest of the game.
Denver faces top-seeded North Dakota State in the semifinals on Monday.