ORONTO - With a little encouragement from former coach Rick Pitino and a little Ukranian superstition, Vitaly Potapenko has pushed and positioned himself as one of the Celtics' top rebounders. In 18.7 minutes per game, Potapenko is averaging 5.3 points and 5.3 rebounds. Last season, Pitino told Potapenko to think of offensive rebounds as ''assists for a big man.'' This season, Potapenko has found a niche on both ends by playing aggressively.

''V brings such a professional frame of mind to what we do,'' said Celtics coach Jim O'Brien. ''He's always ready. He takes great pride in his condition. You never hear a peep out of him. You can turn to him and say, `V, you've got to start. V, go in the game.' You know you're going to get a hard effort and a tough-minded presence on the basketball court.''