Dela Cuesta fired eight of his 18 points in the fourth quarter to power the Jewels to their eighth victory in 10 outings, ahead of the Toyota Otis Sparks and the Rain or Shine Elasto Painters with 7-3 (win-loss) cards.
Preparation was the key to Montañas latest victory.
"We really prepared for this game and the boys responded well to the gameplan," said Montaña coach Nel Parado.
The Spinners, the Heroes Cup champions, reeled to their sixth loss against four wins to remain at fifth spot.
Earlier, TeleTech bucked a sputtering windup as it survived Granny Goose, 76-74, to keep its flickering quarterfinal hopes alive.
Ty Tang, enlisted early in the conference to provide backcourt stability, drained a crucial jumper down the stretch to seal what was only the Titans second win in 10 games.
Tang, a former La Salle standout, finished with 11 points in ending the American-owned call center franchises six-game losing skid.