Velasco, son of 1996 Olympic silver medalist in boxing Onyok, has only made one three in 13 attempts before sinking the open trey from the top-of-the-key. He finished with 12 points.
In the other semifinals game, three-time defending champion San Beda edged fourth seed Letran, 61-57, to clinch a Finals berth.
Arvin Tolentino notched 19 points and 16 rebounds for the Red Cubs, who will play the Staglets in a best-of-three championship series on October 18 at the SM Mall-of-Asia Arena.
Michael Calisaan led no.2 San Sebastian with 23 points on 11-of-14 shooting from the field to go along with 19 rebounds.
Rey Nambatac had an all-around game with 24 points, six rebounds, three assists and six steals while John Quinto, the would-be rookie MVP had 21 points, 12 rebounds and four assists in a losing cause for the Squires, who only converted one three-pointer in 11 tries.