Celtics coach Jim O'Brien isn't surprised by the recent strides made by the Memphis Grizzlies. O'Brien views Memphis as a fast-developing team with talented newcomers who have received considerable experience from the outset. That makes the Grizzlies a dangerous opponent, as the New York Knicks and Los Angeles Lakers discovered in losses to Memphis on Thursday and Friday.

``You're going up against (Pau) Gasol and (Shane) Battier, two outstanding rookies who are starting, playing a lot of minutes and producing,'' O'Brien said before the Celtics narrowly escaped with an 85-80 win over the Grizzlies last night at the FleetCenter. ``These are two talented and hard-working guys who have already played about the equivalent of a full college season if you take into account the exhibition and regular-season games. In that sense, they're really no longer rookies.''