BOISE, Idaho (AP) — Zach Norvell Jr. hit the go-ahead 3-pointer with 20.8 seconds left to help Gonzaga escape a major scare in the West Region on Thursday with a 68-64 victory over UNC Greensboro.

The fourth-seeded Bulldogs (31-4) trailed 64-62 with 1:48 left after squandering a 12-point lead they took early in the second half.

Josh Perkins tied the game at 64, and after Greensboro’s Francis Alonso forced up a miss, Gonzaga got the rebound and worked the ball to Norvell, a redshirt freshman, who spotted up from the right elbow and made the 3 for the lead.

Alonso got called for an offensive foul on the next possession, but Gonzaga’s Rui Hachimura missed a pair of free throws. Marvin Smith had a chance to tie it and his 3-point attempt looked spot on, but it bounded in and out. Norvell made one more free throw to ice the game and finish with 15 points.

Gonzaga, in its 20th straight NCAA tournament, won its first game of March Madness for the 10th straight year, though that’s not the mission anymore for the Zags. They made the national title game last season and came into March playing well enough to make another run.

They ran into a grinder of a defensive opponent in the 13th-seeded Spartans (27-8), the Southern Conference champs who held Gonzaga to 37 percent shooting in the first half, but couldn’t make many shots of their own: they went 0 for 13 from 3 over the first 20 minutes.

Things opened up in the second, and behind Alonso and Troy Demetrius (16 points each), UNCG chipped away, finally taking the lead on Jordy Kuiper’s tip-in.

After a missed Gonzaga free throw, the Spartans had a chance to extend the lead, but Demetrius couldn’t connect on an alley-oop pass to Smith. That turnover, UNCG’s 13th of the game, led to the Perkins basket, and Gonzaga finished the game scoring the final six points.