After trailing by as many as 12 points in the first half, the Commodores (7-2) took control with a 16-2 run early in the second half.
LaChance had five 3-pointers as he hit 8 of 12 from the floor. He was named Southeastern Conference Freshman of the Week after scoring 26 points in Saturday's win over Purdue.
"He loves the fight," Commodores coach Kevin Stallings said. "He walks towards the fight. I like guys that walk towards the fight. I'm not big on those guys that walk away from it."
James Siakam, a senior forward, added 20 points and seven rebounds off the bench.
Damian Jones, a 6-foot-10 sophomore who entered the game as the SEC's third-leading scorer, added 16 for the Commodores.
"(Damian) is our best player," LaChance said. "In the first half we didn't do a very good job of getting him going. In the second half we really wanted to get the ball inside and get it to him."
Vanderbilt started to pull away after a seven-point possession with 8 minutes left after a technical foul on Western Carolina's Justin Browning.
Rhett Harrelson led the Catamounts (3-7) with 22 points, including six 3-pointers, and Torrion Brummitt scored 17. Mike Brown scored 14.
Vanderbilt fans booed whenever Harrelson touched the ball after he had a fiery verbal exchange with Commodores guard Wade Baldwin IV late in the first half.
"We got in a little foul trouble in the second half and their depth is a little bit more than ours," Western Carolina coach Larry Hunter said. "(Vanderbilt) shot the ball very well in the second half."
It was the most points Vanderbilt has scored since a 102-76 win over Mississippi in 2012.
Vanderbilt's bench outscored Western Carolina's 33-15, and the Commodores outrebounded the Catamounts 34-18 and hit 38 of 43 from the foul line.
Vanderbilt took its first lead, 47-46, since early in the first half when Damian Jones sank two free throws with 18:14 left.
Western Carolina broke a 12-all tie with an 8-0 spurt to take a 20-12 lead midway through the first half.
The Catamounts, who made their first five 3-point attempts, expanded their lead to 28-16 when Harrelson buried his fourth straight 3-pointer.
Western Carolina led by 10 when the Commodores closed with a 13-6 run, narrowing the gap to 44-41 at halftime. It was the most points Vanderbilt has allowed in the first half all season and only the second time the Commodores have trailed.
Harrelson led the way as the Catamounts hit 62.1 percent of their shots from the floor during the first 20 minutes.
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