Mendoza admitted it wasn’t easy and the victory came with a "little help" from rival coach Joe Lipa as they moved up to third place with a 2-1 card.
Ateneo trailed, 56-63, but rallied behind Enrico Villanueva, Andrew Cruz and Rainier Sison, whose free throws trimmed the gap to a hairline, 66-67, 1:17 left in the game.
The Pioneer Insurers regained possession after Villanueva blocked Ariel de Castro’s attempt but a traveling violation by Edrick Ferrer started a series of lapses.
The big turnaround came when Lipa, complaining of a backing violation he felt committed by Freezer King Ariel Capus, accidentally hit the time-out buzzer out of frustration and was slapped with a technical foul, 12.1 seconds left.
Defending champion Welcoat Paints bounced back from two consecutive losses via a 76-64 win over Hapee Toothpaste in the second game.