Marck Espejo led the Blue Eagles’ upset with 20 points, including three of his team’s final three points to clinch the impressive win.
Espejo had 17 attacks with his last one sealing the match that came after blocking the Bulldogs’ Peter Torres and a hit from the backline that broke a 22-deadlock in the third set.
Edwin Tolentino and Rueben Inaudito had 10 points each for defending champion NU, which absorbed just is first defeat after sweeping the first round with a 7-0 mark.
Earlier, De La Salle repulsed University of the Philippines also in straight sets, 25-18, 25-17, 25-22, to improve to 3-5.
Ateneo, which followed up its 25-19, 20-25, 25-18, 25-15 last Wednesday, upped its mark to 5-3 and remained in third place trailing idle Far Eastern University just half a game in the standings.