Back in late January, Rajon Rondo went down with a season-ending ACL tear in his knee. That, according to Paul Pierce, was the day the Boston Celtics would forever be altered. Per the Boston Herald: “With time growing shorter with every passing game for the old Celtics core and with Rondo’s health uncertain for the upcoming year as he rehabs his knee, Pierce acknowledged that the injury was a big reason why he is now wearing a Brooklyn Nets uniform and not the one he wore for the past 15 years. ‘It would be hard to contend,’ Pierce said on Friday, the last day of his camp at Basketball City in the shadow of the Garden. ‘I saw the vision. I saw all that. As a player, I’m selfish. I want what’s going to be good for me and the team. But you’ve got to look at the management looking at what’s down the road. If it’s up to me I would want to rebuild to win a championship by bringing players in. They were looking at the future, down the line. Rajon might not be here for the beginning of the year or however long he takes, so it would be tough for us to be a contender or get in a position to contend. Everybody saw that and I think that helped the decision on both sides.’ The moves were franchise-altering and they were swift. Doc Rivers was sent to the Los Angeles Clippers in a trade, and on draft night, the framework of a megadeal was put in place with Brooklyn. Pierce, Kevin Garnett and Jason Terry were moved to Brooklyn officially after the July moratorium was lifted, and the Celtics got back Kris Humphries, Keith Bogans, MarShon Brooks, Gerald Wallace, three future first-round draft picks and the chance to start over. Add the surprise hiring of Celtics coach Brad Stevens, and in just a few weeks the Atlantic Division looked a whole lot different. ‘It was like a domino effect,’ Pierce said. ‘It was like (the Rondo injury) was there and then Doc. When you put all that stuff together, you know the writing was on the wall.’ The chance to get another ring was important for Pierce and rebuilding was not. The second-leading scorer in Celtics history is hoping his presence — along with that of Garnett, Terry and Nets head coach Jason Kidd — can bring that same kind of championship mettle to his new team, because time is running out. ‘It’s a lot shorter,’ Pierce, who played in 1,102 games with the C’s, said of the window to win in Brooklyn. ‘I think this might be like a two-year window right now. I have one year left on my deal, but I know KG probably plans on retiring in two years. I feel like you got players of our caliber and players that can change a culture and do so many things on and off the court to help the ballclub. It’s really based on that.’”