The Lobos improved to 7-0 with Kirk hitting 6-of-8 from the field, scoring 16 points and hauling in 13 rebounds. He also blocked three shots.
New Mexico had a six-point lead with 11:38 to play, but over the next 5:26 Mercer could manage only three points.
Cameron Bairstow contributed 16 points for the Lobos, who outrebounded the Bears by 13.
Mercer (3-4) got 16 points from Travis Smith and 10 from Jakob Gollon.