Louie Sangalang put the finishing touches in the win with his three-point play in the final 46.6 seconds to cap off his 21-point, 5-rebound performance.
Fran Yu added 10 points on 7-of-9 shooting from the free throw line, on top of seven rebounds and three assists, and Kurt Reyson got nine points, six dimes, and five boards in the win.
At 13-4, Letran is assured of at least a playoff for a top two spot, and can gain the twice-to-beat incentive outright in its last game against Jose Rizal University on Wednesday.
"Gusto naming mag-No. 1 syempre. Bahala na kung sino yung makatapat," said assistant coach Raymund Tiongco as coach Bonnie Tan was placed under health and safety protocols.
The Knights were happy to share the rock in this game, dishing out 26 assists which translated into a potent 46-percent shooting from the field in this Finals rematch.
"Nag-adjust lang kami sa nangyari sa San Beda. Nagyon mas maganda yung ball movement namin," said Tiongco, with the defending champions still seething from their 91-77 defeat to the Red Lions last Wednesday.
Paolo Hernandez paced the Cardinals with 13 points and five boards, as Warren Bonifacio and Jeric Pido scored eight each.
Mapua dropped to 6-11 for the season with one more game against San Sebastian on Wednesday.
Letran 74 - Sangalang 21, Yu 10, Reyson 9, Caralipio 8, Javillonar 8, Ariar 6, Monje 4, Olivario 3, Guarino 3, Paraiso 2, Santos 0.
Mapua 58 - Hernandez 13, Bonifacio 8, Pido 8, Nocum 6, Cuenco 5, Lacap 5, Soriano 4, Garcia 3, Salenga 3, Agustin 3, Mercado 0.
Quarterscores: 22-18; 46-32; 60-53; 74-58.