The Flames -- only the second team ever to make the NCAA tournament with 20 losses -- had a chance to win it. John Caleb Sanders drove coast to coast and flipped up a left-handed layup in heavy congestion that just missed. A&T (20-16) rebounded and, while Sanders rolled in pain on the baseline, began to celebrate an end to more than 30 years of disappointment.
Underwood came in averaging just over 6 points, but was perfect from the field, hitting six field goals in as many attempts. Bruce Beckford added 16 points and Lamont Middleton 14.
The victory advanced the Aggies to a showdown with top-seeded Louisville (29-5) in Lexington, Ky., Thursday.
Davon Marshall had 22 points and Sanders 21 for Liberty (15-21).
A&T came into the game 0-9 in NCAA tournaments, and hadn't come close to making the elite field since their last trip in 1995.
With the Aggies holding onto a 42-39 lead early in the second half, the teams put on an offensive display that got the capacity crowd into the game.
Liberty scored on five consecutive possessions, making all five shots from the field, while A&T countered by hitting four shots in a row. The last bucket in the sequence, Marshall's 3 from the right side, narrowed the gap to 52-51.
After Jean Louisme ended both streaks -- missing a shot and then stealing the ball at the other end -- Austin Witter hit a rebound follow.
The pace slowed considerably, more to A&T's liking. Underwood made two shots then drove the lane and hit a lefty layin. Seconds later, Adrian Powell swished a 3 from the left corner and the lead was suddenly back to 10 at 61-51.
By that point, Liberty had not scored in almost 6 minutes, missing seven straight shots from the field.
The Flames rebounded to get as close as four points, then the Aggies stretched it back to eight before Sanders scored on a three-point play in traffic and then made a 3 to make it 71-67.