BOSTON To Doug Collins, Boston 's Big Three is already a memory. ''I don't look at them as the Big Three. I look at them as the Championship Four,'' the Philadelphia coach said. ''Because if you're going to leave Rondo out, you're making a huge mistake.'' Rajon Rondo helped his aging teammates keep their season going Saturday night, finishing with 18 points, 10 assists and 10 rebounds in Game 7 against the 76ers to lead Boston to an 85-75 victory and into an Eastern Conference finals matchup with the Miami Heat. The Celtics will open the third round of the NBA playoffs in Miami on Monday night. ''I've already packed,'' Celtics coach Doc Rivers said. ''We'll be ready. It's going to be a tough turnaround, but we're not an excuse team. We'll be ready on Monday.'' Bouncing back from his worst game of the playoffs - and snapping out of a 32-minute slump in which he had j...