Riordan paced the Storm (11-7, 5-5 American Rivers Conference) with 19 points and four assists, while classmate Reiter scored 10 points, grabbed 17 boards and swatted four shots. Riordan scored 12 points in the second half off of 4 of 7 shooting from the field.
Both teams were tied 35-35 going into halftime before Simpson erupted on a 13-3 run to begin the second half, which gave the home team some breathing room. Riordan made two 3-pointers during the run and went 60-percent from deep during the game.
The Spartans (11-9, 4-7 A-R-C) went on a short rally and got back to within nine, before Simpson went on another run of 11-3 to pull away.
The Storm had a slim-seven-point advantage in the opening five minutes of the game and that would be their largest advantage in the opening 20 minutes of play. For the last 10 minutes of the period, no team would garner a lead bigger than five points.
Both teams were equal on the glass with 35 rebounds, with Dubuque holding a 15-6 offensive rebounding margin.
Reiter earned a career-high in rebounding tonight and is now tied for a game-high in the conference this season. Kyle Wagner contributed 16 points on 4 of 6 shooting from behind the arc. Wagner is fourth in the country and first in the conference in 3-point percentage with a 52.2 percent clip for the year.
Marcus McDaniel led the Spartans with 21 points.
Simpson shot 50-percent from three for the fifth time this year and are 5-0 when doing so. Each team had 12 attempts at the free throw line, while the Storm made 10 and the Spartans made four.
Simpson remains home when Wartburg visits on Wednesday for an 8 p.m. matchup inside Cowles Fieldhouse.