SAN JOSE, Calif. — Two months ago, Xavier lost its point guard, one of its top scorers, to a season-ending knee injury.

Three weeks ago, Xavier lost its sixth consecutive game, barreling toward a hollow March.

Two weeks ago, Xavier upset Butler in the Big East quarterfinals, a victory that maybe, just maybe, nudged the Musketeers into the N.C.A.A. tournament field.

On Thursday night, Xavier, the lowest seed of the 16 teams to advance out of the second round, became the lowest seed to advance to the regional final. The No. 11 Musketeers stunned No. 2 Arizona, 73-71, overcoming an 8-point deficit in the last three and a half minutes. When it was over, when Malcolm Bernard yanked down a rebound and dribbled out the final three seconds, the Musketeers flexed in front of their fans, climbed onto press row and screamed in euphoria.

Trevon Bluiett, who led Xavier with 25 points and assisted on Sean O’Mara’s game-winning basket, said his impulse was to run into the crowd.