"He's a little bit of an unlikely looking guy, but he's got some dirty in him -- a good dirty and some nasty," Commodores coach Kevin Stallings said. "I like Riley. He just kind of has a knack and he doesn't have much fear. He's a fearless kid that really believes in himself."
LaChance hit 9 of 13 from the floor, including three 3-pointers, and all five of his foul shots. His last 3-pointer came from 37 feet to give Vanderbilt a 72-58 lead as Purdue was mounting a comeback.
It was the most points by a Vanderbilt freshman since A.J. Ogilvy scored 27 against Auburn in 2008.
"I had a bad shooting game last game," LaChance said of a loss to Baylor. "I just got in the gym and went back to the fundamentals and worked on the basics. My teammates did a great job of setting me up and giving me open looks."
Purdue couldn't find a way to contain LaChance.
"Riley LaChance, like I said, is the difference in the game," Boilermakers coach Matt Painter said. "He was great. When you allow him to get a couple looks, he can really shoot the basketball and get into a rhythm."
Vanderbilt (6-2) ended a four-game losing streak against the Big Ten, earning its first win since an NIT victory over Indiana in 2005.
It was Vanderbilt's first game in nine days after taking time off for final exams.
Vanderbilt's Damian Jones added 15 points and James Siakam had 12.
It was the first road game for the Boilermakers (8-3), who are 6-1 at home and 2-1 on neutral courts.
Purdue is 6-16 on the road during the last two seasons, including losses in its last seven away games last year.
It was the first meeting between the schools since Vanderbilt beat Purdue in 1965.
Rapheal Davis led four Boilermakers in double figures with 15 points. Isaac Haas added 13, Kendall Stephens had 11 and Bryson Scott had 10.
The Commodores hit 9 of 14 from beyond the 3-point arc.
Vanderbilt made a 15-3 run early in the second half to stretch its lead to 60-40. Purdue coach Matt Painter called a timeout after Matthew Fisher-Davis' 3-pointer gave the Commodores a 20-point lead.
Jones scored the Commodores' first six points on a layup, jumper and dunk.
There were five lead changes after that before Vanderbilt went on a 12-4 run to take a 23-16 lead.
The Commodores expanded their lead to 43-32 by halftime with LaChance, Siakam and Jones leading the way.
It was the most points scored by Vanderbilt in the first half this season as the Commodores shot 63 percent from the floor in the first 20 minutes.
Both teams featured young lineups that each included three freshmen starters.
Vanderbilt freshmen guards Wade Baldwin IV and Shelton Mitchell helped generate offense from the backcourt with six assists apiece.