The Huskies (1-0), who went 9-22 last season and 2-16 in the Pac-12, leading to the firing of Lorenzo Romar, trailed 72-63 with 4:57 left before storming back against the team picked to win its third straight Ohio Valley Conference championship.
Nowell kept answering every Belmont basket and basically put the game away with two free throws with eight seconds remaining.
He went 12-for-18 from the floor and also grabbed five rebounds in 36 minutes.
David Crisp scored 16 points, hitting two big free throws with 22 seconds remaining and overcoming a 2-for-8 shooting night by going 10-for-13 from the foul line. Matisse Thybulle added 13 points, including two free throws to officially put the game out of reach in the final seconds, while Carlos Johnson had 10 points and five rebounds.
The Huskies, who went 26-for-36 from the foul line while Belmont (0-1) attempted just 12 free throws, were picked to finish 10th in the conference by the league media.
The Bruins, who had a 14-game winning streak but had to settle for the NIT when they lost in the conference tournament, were 15-1 in their league last season.
Nick Hopkins led Belmont with 22 points. Dylan Windler posted 18 points and 11 rebounds and Amanze Egekeze 17 points in the tough loss.
The Huskies host Eastern Washington Sunday, while the Bruins return home for Vanderbilt on Monday night.