Derrick Brown led the Musketeers (25-5, 13-2) with 18 points. No other player was in double digits.
Xavier's only two A-10 losses came in Philadelphia, the other a 78-59 loss on Jan. 16 at Temple.
The Hawks will play next season at the Palestra while the antiquated fieldhouse undergoes sorely needed renovations, including new locker rooms and 1,000 more seats.
The Hawks could return for a home game in the NIT, but whatever happens in the postseason will merely be a footnote to one of the biggest wins in the steamy and cozy 3,200-seat gym.
Perhaps having Nelson, now with the Orlando Magic, sitting at the end of the bench as an honorary captain brought some good luck to the Hawks. After all, he was a senior and Wooden Award winner when the Hawks started 27-0 in the 2003-04 season, and a banner in the pregame ceremony read, "Jameer Brings Magic to the Fieldhouse."
Whatever the inspiration, the Hawks played like a team determined to return to the NCAA tournament for the first time since Nelson helped them all the way to regional final four years ago.
The Hawks broke this one open early in the second half and grabbed a 15-point lead. The raucous crowd was chanting and stomping all game, feeling extra juiced after a pregame ceremony that brought back so many former Saint Joseph's greats.
Rob Ferguson, who scored 13 points, sank a 3-pointer early in the second half for a 10-point lead, and Ahmad Nivins converted a tough inside basket and free throw for a three-point play in front of the student section.
Tasheed Carr fell on his back after he sank a 3 from the top of the arc and Nivins' baseline dunk made it 46-31, with all those big baskets becoming important down the stretch.
Xavier made a spirited run in the final minutes that nearly spoiled all the festivities. Josh Duncan sank a 3 with 15.5 seconds left that cut the deficit to 67-63. Drew Lavender, severely limited the last five games because of a sprained left ankle, hit another 3 with 7.1 to go that made it 69-66.
But the Hawks sealed the win at the line, with the students bellowing their famed chant, "The Hawk Will Never Die!" They rushed the court and danced with the Hawks one final time.
Saint Joseph's created a list of its 25 most memorable fieldhouse games - dating back to the first one on Nov. 26, 1949 - but it surely needs some updating now. One game that could get bumped? The previous biggest upset, an 81-80 win over No. 10 Massachusetts on Feb. 15, 1994.
The Hawks went on an 11-2 run and Calathes hit a running jumper in the final minute of the first half to give them a 33-26 halftime lead.
