Twenty of Mustard's points came in the first half, helping the Sioux (7-3 overall) take a 37-23 lead at the break.
Early in the second half, North Dakota went on a 16-3 run, holding the Bears (6-3 overall) without a field goal for more than nine minutes during the stretch. Northern Colorado didn't come closer than 14 points the rest of the game.
North Dakota held the Bears to 40 percent shooting from the field and forced 16 turnovers.
Michael Allen, with 15 points, was the only Northern Colorado player in double figures.
Hunter Berg added 12 points for North Dakota.
The victory gave Sioux coach Rich Glas his 200th win in 11 seasons at North Dakota.
NORTHERN COLORADO (6-3): Roenn 1-4 0-0 3, Martinez 2-4 0-0 5, Elize 3-9 2-4 8, Allen 6-11 1-2 15, Britt 2-5 2-2 6, Caton 0-2 1-2 1, Hansen 1-4 0-0 2, Grable 1-2 2-2 5, Sehringer 1-4 2-2 4, Adle 3-5 3-6 9.
NORTH DAKOTA (7-3): Jacobson 2-3 0-0 6, Berg 4-6 4-5 12, Larson 1-1 0-0 3, Sheplee 0-0 0-0 0, Travis 3-8 3-3 9, Ristvedt 1-3 0-0 2, Mustard 9-12 11-14 29, Bernhardt 1-1 0-0 2, Badding 1-1 2-2 4, Reinke 1-5 4-6 6, Behrens 1-8 5-6 7
Halftime: UND 37, UNC 23. 3-Point goals: UNC 5-13 (Roenn 1-4, Martinez 1-2, Elize 0-1, Allen 2-3, Caton 0-1, Grable 1-2), UND 3-9 (Jacobson 2-3, Berg 0-1, Larson 1-1, Travis 0-2, Ristvedt 0-2). Fouled out-UNC Britt. Rebounds-UNC 27 (Allen 7), UND 36 (Behrens 9). Assists-UNC 10 (Martinez 4), UND 15 (Berg 5). Total fouls-UNC 22, UND 16. A-2,634.