Garner went 13-of-17 from the field.
Jamal Olasewere provided a double-double of 15 points and 10 rebounds as the Blackbirds (20-13) collected their straight NEC Tournament championship. Kenny Onyechi helped out with 11 points and seven rebounds.
The Mountaineers (18-14) got 21 points from Sam Prescott but still saw their nine-game winning streak broken.
Shivaughn Wiggins (11 points), Rashad Whack and Julian Norfleet (10 apiece) also reached double figures for Mount St. Mary's.