Nielsen came within a rebound her fifth consecutive double-double and Reeves scored 11 of her career-high 14 in the first half as the Storm (13-1, 3-0 Iowa Conference) won their 17th regular season home game in a row.
Holly Halstead had 18 points and Baileigh O'Brein brought down 13 rebounds for the Knights (9-5, 2-1), who entered the game as one of three remaining unbeaten teams in the Iowa Conference.
Wartburg's aggressive, full-court defense kept Simpson off-balance, forcing the Storm into a season-high 23 turnovers. But the Storm took advantage of the aggressive defense by making good on 21 of 29 free throw attempts. Nielsen led the way by making 8 of 9.
Chelsie Rohrs found a streaking Annie Gullickson for a layup that beat the clock at the end of the first half as Simpson outscored Wartburg 10-2 in the final three minutes. A layup by Brooke Panzer sparked the run, which broke a 21-21 tie and gave the Storm a 30-23 lead at halftime.
Reeves stretched the lead to 10 with a 3 to open the second half and Wartburg couldn't get closer than five the rest of the way.
Rohrs finished with 10 points and Nicole Crisp led the defense with four steals.
Simpson hosts Loras next Wednesday, Jan. 16 at 6 p.m. The Duhawks (12-2, 2-1) knocked off preseason favorite Coe 59-56 on Saturday, leaving Simpson alone atop the league standings as the only unbeaten team in conference play.