The Jewels rallied behind Magpayo after the 6-foot-3 forward suffered a broken right hand on a bad fall late in the first quarter, outplaying the league newcomers at crunch time for a good start in the tourney.
"This one’s for Al," said Montaña coach Robert Sison.
Eric dela Cuesta pumped in 19 points, including nine in the fourth quarter, as the Jewels overcame a huge deficit to force the overtime at 69-all.
Montaña closed out with a 7-0 blitz in regulation play.
Earlier, Dennis Concha made 12 of his game-high 16 points in the fourth quarter, fuelling a searing Granny Goose Kornets breakaway en route to a 62-49 whipping of Bacchus Energy Drink.
The Snack Masters started out flat and needed Concha’s fourth-quarter exploits, including 10 straight points made in a key stretch, to open their campaign in the tourney on a winning note.