Defense spelled the difference in Game 1 of the University Athletic Association of the Philippines Season 85 men's basketball tournament best-of-three finals series.

In a chess match between two of the league's top tacticians, it was defending champion University of the Philippines head coach Goldwin Monteverde who drew the winning strategy that put his squad on the cusp of making a repeat.

The Fighting Maroons threw the Blue Eagles out of their rhythm with swarming defense, especially in the closing minutes of the fourth quarter, leading to a 72-66 victory in the series opener late Sunday at the Mall of Asia Arena.

Timely stops saved UP from a dry spell of more than three minutes as Ateneo was making a desperate run to comeback from a 10-point deficit.

"Going towards the game, we prepared for Ateneo. We know what kind of team Ateneo is. We really can't relax. We always talked about it, that playing against Ateneo, we should play really good defense," Monteverde said.

The Fighting Maroons kept pressuring the ball handlers of the Blue Eagles. They effectively clogged the driving lanes and even limited Ateneo's points in the paint to just 24.

Ateneo big man Ange Kouame had 15 points but shot 5-of-12 from the field, Dave Ildefonso even had a harder time with 3-of-12 shooting clip while forward Kai Ballungay was a non-factor on offense as he missed all his three shots.

"Actually, we also had some lapses but the good thing, even before, the team does not stop and they would always communicate to address those lapses. We were able to sustain it until the end of the game," Monteverde said.

Blue Eagles mentor Tab Baldwin acknowledged that the Fighting Maroons did a great job disrupting if not stopping their offensive flow.

"Execution during the whole game was difficult because the pressure from UP was really good," he said.

Ateneo turned the ball over 15 times that the opposing team converted to 10 points.

The Blue Eagles, who were outrebounded, 45-49, also allowed the Fighting Maroons to pick their pockets with eight steals.

UP's defensive prowess was in full display when Zavier Lucero, who had a double-double of 14 points and 11 rebounds, blocked the two-handed slam dunk attempt of Chris Koon that sparked its 10-2 scoring blitz capped by Harold Alarcon's step back triple to beat the shot clock buzzer for a 68-58 lead in the last 4:38.

"Yeah, I think, our team is, you know, as coach always said in practice, its five versus one on the floor so anytime there's an opportunity to help, if somebody gets beat, it's on us to be there for those guys to make sure that nobody gets left on an island, so, yeah, that was just me on the right place at the right time," Lucero, who had two blocks — all coming on the crucial stretch — said.

"But I mean, all our guys made plays, stepped up. I mean, after I blocked Chris, Harold hit a big three for us, so, it was a team effort tonight for sure."

UP weathered a late uprising by Ateneo after going up, 70-60, with 3:46 left.

The Blue Eagles scored six straight points to move close within four but JD Cagulangan made a good defensive stop as he stole the ball from Koon.

Lucero then swatted Kouame's shot in the next play before Cagulangan iced the game with a pair of charities.

Now with just a win away from hoisting another championship, expect the same defensive effort from the Fighting Maroons in Game 2 on Wednesday at the Smart Araneta Coliseum.