Fort Collins, CO – Dorian Green scored 17 points and Pierce double, as Colorado State knocked off No. 18 63, at Moby Arena.
Hornung logged 13 points and 15 rebounds, while Wes Eikmeier added 11 points in Colorado State's second straight win.
The Rams (17-9, 6-5 MWC) improved to 13-1 at home and have an opportunity to make a case for NCAA Tournament consideration with matchups against nationally-ranked San Diego State and UNLV on the horizon.
New Mexico (22-5, 8-3) had won seven in a row to climb into the rankings for the first time since the end of the 2009-10 season, but a 37-percent shooting effort did in the Lobos on Tuesday.
Kendall Williams had a team-high 16 points, but shot just 3-of-13 from the field in defeat.