Marin Maric added 14 points and 11 boards for the Huskies (6-0), which shot just 35 percent from the field but controlled the glass 41-33. Armstead hit nine of his 11 from the free-throw line.
Northern Illinois took the lead for good during a 12-2 run stretching across both sides of the break that was capped by Marshawn Wilson's 3-pointer, making it 41-34 with 14:41 to play. The gap widened to 12 with Levi Bradley's layup midway through the second half before Idaho battled back, cutting it to 63-59 on Victor Sanders' 3-pointer with a minute to play.
Maric and Jaylen Key then sealed the win at the free throw line.