The Ateneans led by as many as 20 points behind the hot hand of Michael Javelosa, who finished with 16 points. But a fiery SBC comeback trimmed the deficit to only six in the last 30 seconds.
Ateneo will dispute the SBP title with La Salle Greenhills, which toppled Xavier School, 48-38, in the other semifinal match.
Thomas Torres banged in eight of his game-high 16 points in the payoff period to propel LSGH to the finals.
San Beda avenged its SBP loss by beating Ateneo, 68-59, in the Passerelle semifinals.
The Bedans advanced to the finals against De La Salle Zobel, which walloped Xavier School, 59-48, in the other semifinal contest.
After a sluggish start, the Red Cubs tightened their defense and improved their offense to take control the rest of the way.
Ralph Mendoza sparkled for San Beda with 13 points while Al Bugarin led Ateneo with 11.
Final matches will be played on Sunday, Spet. 10 at the Ateneo gym in Loyola Heights.
It will be Ateneo against Xavier at 8 a.m. followed by San Beda against Xavier for third place in the Passerelle and SBP, respectively. The title games start at 11 a.m. between Passerelle teams San Beda and DLSZ, followed by the SBP showdown between Ateneo and LSGH at 12:30.