aul Pierce would not divulge why the Celtics now win tightly contested games in the fourth quarter. With a mischievous grin, he claimed it was a highly guarded franchise secret. Maybe three parts leprechaun and two parts practice. Maybe not.

''If I told you,'' he said, ''I'd have to ...'' But his laughter kept him from finishing the sentence. Despite losing an 18-point third-quarter lead, Pierce and the Celtics could smile about escaping with an 85-80 win over the Grizzlies last night