Actually - Pitino didn't press all the time in the NBA, just turned it on in spots - nothing like the way he ran it in Kentucky....ultimately didn't work well enough other than that amazing first game (upset win over a hugely favored Jordan and the Bulls) - and at times when they adjusted personnel to get players like McCarty who could execute it better.
Pitino's issue was that he installed himself as President and made all personnel decisions along with the worst GM in celtics history - Chris Wallace. It could have been different if he stuck to coaching - but his reputation was so high at the time, he was able to get it all.
They were too quick to jettison useful existing players they really missed like - Eric Williams, Radja, David Wesley, Rick Fox - in exchange for some awful additions like Chris Mills, Knight, Edny, Declerq, etc.
He was better at drafting - Pierce, Billiups, Mercer (solid before his injury), Bruce Bowen was a free agent but an unsigned/undrafted guy who broke in with the Cs.