One of the three players the franchise expected to bring to the PBA, Cabatu struggled in the early going but found his range in the fourth to power the team to victory.
The former La Salle standout was particularly impressive in the closing minute of the contest as he knocked in six straight free throws to seal the win for the Elasto Painters.
"He’s really capable of doing that," said Rain or Shine coach Leo Austria, referring to the son of former pro Sonny Cabatu.
After racing to a 21-10 first quarter lead, the Elasto Painters suddenly turned cold as Ryan Arana sparked a rally that saw the Post Masters snatch a 36-33 at the break.
But Rain or Shine settled down and held Harbour Centre to just four points in the third period before going to Cabatu down the stretch.
Samigue Eman, the prized 6-foot-10 talent from the South, suited up for Rain or Shine but did not see action.
Earlier, Toyota Otis leaned on Fil-Am Joe Devance as it edged Hapee Toothpaste-PCU, 77-73, to post its first opening game win after three conferences.
Devance fired 22 points and hauled down 12 rebounds to steer the Sparks to an inspiring start following disappointing efforts in the last two conferences where they finished dead last.