Lyceum climbed out of a sizable first-half deficit to beat Letran 82-75 on Sunday at FilOil EcoOil Centre in San Juan.
The Knights ended the first quarter up 29-13 and held the game's biggest lead at 19, 40-21, in the second, before the Pirates tightened their defense and turned the tables on the defending champions.
Lyceum, which won its fifth in a row, hiked its record to a league-best 5-1; the Knights, losers of two straight, dropped to an even 3-3, good for a tie at sixth to seventh places with Perpetual Help.
Idle Saint Benilde also has a 5-1 mark.
In their last game on Friday, the Knights wasted away a 16-point first-quarter lead before falling to San Beda.
Mclaude Guadaña finished with a career-high 20 points, John Barba added 12 points and 8 rebounds, and Patrick Montano contributed 12 points and a pair of 3-pointers to pace the Pirates, who saw alumnus and former league MVP CJ Perez at the arena.
Lyceum used a 14-2 run in the third quarter to seize the lead 49-48, as both teams went back and forth.
With the game tied at 73, Barba broke the deadlock with a straight-away triple, before Guadaña made four straight free throws to seal the deal.
In that stretch, the Pirates' defense forced the Knights to shoot and miss an ill-advised 3-pointer, and turn the ball over twice.
Fran Yu, who had 10 points in Letran's blistering first quarter, led the Knights with 18.
Letran was without key players Brent Paraiso and Louie Sangalang, who served the second of an upgraded two-game suspension.
In Letran's game against Mapua on Tuesday, Paraiso was ejected when he was adjudged a disqualifying foul for "an act of violence," and Sangalang when he was slapped with two technical fouls.
The two Knights were initially docked a game, but league commissioner Tonichi Pujante made it two after reviewing the infractions.