Junior guard Kameron Williams added 13 points and Phil Lawrence provided 12 as the Gaels' balance offset a 29-point effort from Spalding senior guard Greg Brown. Mount St. Joseph improved to 26-6 on the season and will seek the program's fourth BCL championship Sunday.
After Williams got a steal and layup to beat the halftime buzzer and give the Gaels a 20-17 advantage at the break, Booth took over to start the third quarter. He scored Mount St. Joseph's first eight points — converting a three-point play and adding a 3-pointer and another long jumper before Williams made a three-point play to give the Gaels a 31-20 lead with 4:27 to play.
But the Cavaliers — behind the hot shooting of Brown — climbed back into the game and would get within three points twice in the fourth quarter.
Brown scored 22 of his 29 in the second half, and his fifth 3-pointer with 46 seconds left cut the Gaels' lead to 52-49.
Booth had the final say at the defensive end when he blocked Malik Harris' driving layup try with 27 seconds left. Lawrence hit two free throws with 26 seconds remaining for the final margin, with Brown missing two hurried 3-point tries in the final seconds.
The Cavaliers, who made their first semifinal appearance since 2004, finished the season with a 17-15 mark.
AS—Grant 5, Brown 29, Dalce 2, Jefferson 4, Potts 7, Harris 2. Totals: 19 5-8 49.
MSJ—Lawrence 12, Booth 19, Williams 13, Jones 6, Long 2, Adams 2. Totals: 19 14-16 54.
Half: MSJ, 20-17.