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.
But who else made the play of the game but Underwood. He drove and was fouled with 1:49 left and popped in both free throws for a six-point advantage.
The Flames made it tight, however. Marshall threw in a 3 from the last inch of the corner with 1:32 left, then with 11.2 seconds left he scored again on a baseline drive to narrow the lead to 73-72.
With 7 seconds left, Middleton was fouled but missed the front end of the bonus situation, setting the stage for Sanders' wild race against the clock while going coast to coast.
Liberty was only the second team to ever come into the tournament with 20 losses, matching Coppin State (16-20) in 2008. Amazingly, the Flames opened the season by losing their first eight games. Despite two players quitting the team during that discouraging period, others stuck it out and persevered.
Still, they were run out of their own gym in their final home game, 83-68 by VMI, to fall to 10-20 on the season.
But then came an incredible run through the Big South tournament including playing, and beating, both of the divisional leaders during the season. Their 87-76 upset of Charleston Southern in the conference title game on March 10 assured them of the Big South's automatic spot in the tournament.
A&T has a glittering, if now faded, legacy. The Aggies made it to the NCAA tournament seven years in a row 1982-88, but had fallen on hard times. They piled up 15 consecutive losing seasons until their late hot streak this year in the conference tournament pushed them above .500.
They were headed nowhere just 12 days earlier, after a loss at home to Norfolk State in their regular-season finale dropped them to 15-16.
But they roared through the Mid-Eastern Athletic Conference tournament, winning each of their first two games by double-figure margins and then showing some poise down the stretch of the semifinal and final to win close games against Delaware State and Morgan State, respectively.
They shot 58 percent from the field (15 of 26) in taking a 40-33 lead at halftime. They fell behind 9-2 early while making only one of their first four shots from the field, but then found the range against a cloying, scrappy Liberty defense.
Down 22-20 midway through the opening half, Witter touched off a rapid-fire 10-0 run with a go-ahead 3 from the top of the key. Beckford hit a 10-foot jumper and then scored inside. Then, after Liberty's third misfire in a row, Underwood -- who was a perfect 3 for 3 from the field for eight points in the opening half -- hit a 3 from the left wing while falling down to make it 30-22.
After Joel Vander Pol hit a free throw then rebounded his own miss, Speaks drove the right baseline for a basket.
But A&T countered on a Beckford reverse layup after recovering his own blocked shot. Middleton then made a pair of foul shots and added a perimeter jumper from the left wing to make it 36-25.
That 10-point spurt was part of a span where the Aggies scored on eight possessions in a row while turning a one-point deficit into the 11-point lead.