“We want to stay as big as possible, what we didn’t like with Jason in the [starting] lineup was — now we’re going to play him every night — and when he and Kevin were off the floor, we got small quickly,” Rivers explained. “This way we can keep a big on the floor at all times.
“We could have done it the other night, but that was Avery’s first night. That is the group that helped us. But having Jason [play every night] will help Kevin, because he still won’t have to play ‘5’ the entire time. I just think the season’s too long now for Kevin to do that.”
The Celtics are also hoping the move will motivate Bass, who is averaging just 8.1 points and 5.3 rebounds a game.
“That’s what we’re hoping,” Rivers added. “You don’t do it just for the group, you do it for the individual at times,” said Rivers. “Brandon’s played better when he’s playing with Kevin, though everyone has for that matter. I think clearly Brandon has. And that’s one of the reasons we are doing it.”
The lineup of Rajon Rondo , Avery Bradley , Bass, Kevin Garnett  and Paul Pierce  marks the ninth different lineup Rivers has used in the first 32 games of the season. That lineup debuted on March 25, 2012 after Mickael Pietrus  suffered a concussion in Philadelphia and two games after Ray Allen  was sent to the bench. With that lineup, the Celtics went 11-3 down the stretch to help the Celtics win the Atlantic Division title for a fifth straight season.
Collins had started the previous seven games for the Celtics since being inserted in the lineup for Bass on Dec. 21 against the Cavaliers  to take the load off Kevin Garnett in the low post.
Bass has strugged in his role off the bench, both offensively and defensively, and Rivers made the decision Friday to boost Bass’ game by putting him on the floor more with Garnett.