By Brian Robb, CBS Boston

BOSTON (CBS) – In the midst of a season filled with roster turnover, Gerald Wallace has been a constant leader for the upstart Celtics behind the scenes. The 32-year-old veteran has watched most of the Celtics’ recent success from the sidelines, but has provided stability for the team’s young core during a year of constant change.

On Sunday night against the Pistons, Wallace got a rare chance to see some extended floor time, as Brad Stevens looked to him for a spark with both Isaiah Thomas (back) and Marcus Smart (suspension) out of the lineup. The 6-foot-7 forward provided some useful grit, grabbing eight rebounds in just 12 minutes of action in Boston’s 105-97 overtime loss to the Pistons.

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The defeat was a particularly painful one for the suddenly-reeling Celtics to swallow. The hosts blew a 10-point second half lead, against a team who is playing for pride and little else at this stage of the season. With a challenging schedule ahead, Wallace took it upon himself to send a bit of a message to a Celtics locker room that has now lost three straight games.

“We’re a little bit too late in the season to be losing games like this, especially at home,” Wallace declared after the game. “We don’t have disrespect towards Detroit, but this is a game we were supposed to win. We had the opportunity to win. We put ourselves in position to win the ballgame and then in the second half, we let the game get away and that’s something we can’t do. We have to finish out games, especially knowing we have a back-to-back coming up against Brooklyn.”

Wallace’s message carried weight to the members of Boston’s shorthanded roster after the letdown.

“[Wallace has] been through [the playoffs], he knows what it takes,” Jae Crowder said. “We’re a younger team and we have to listen to his leadership.”

Boston’s loss dropped the Celtics in a ninth place tie with the Indiana Pacers in the Eastern Conference playoff race with just 13 games remaining. Currently, five teams, including Boston, are within just 2.5 games of each other in the standings. With only two playoff spots up for grabs within that group, Wallace knows Boston’s margin for error is razor thin in the next few weeks.

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“I told the guys, we got to be more serious because giving games away like this, we don’t have the length of our schedule to make up games. Every game counts for us right now. We got to take it one game at a time and take care of those guys,” Wallace said.

That kind of sentiment was echoed around the locker room following the defeat.

“They played harder than us at the end of the game,” Jonas Jerebko said of his former team. “We didn’t play our kind of basketball for long stretches of the game.  They played hard and they came out with the win. …We’ve got to be better than that.”

“We couldn’t buy a bucket, but still, we had the lead with one possession left in the game,” Crowder added after scoring 19 points in a game-high 44 minutes. “You can say what you want to say [about the circumstances], we were right there to win the game. [Fatigue or missing players] has nothing to do with us losing that game.  We were in position to win that game and we didn’t.”

With just two of Boston’s remaining 13 games coming against teams not fighting for a playoff spot or better playoff seeding, the remaining road to a potential postseason berth will be a serious challenge. Reinforcements are on the way with Smart returning from his suspension Monday night, and Thomas likely to suit up later this week as well after missing the past seven games.

Both players will help, but if the Celtics want to get their young core a taste of the postseason, they must heed Wallace’s advice and take care of business down the stretch of a surprising season.

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Brian Robb covers the Celtics for CBS Boston and contributes to NBA.com, among other media outlets. You can follow him on Twitter @CelticsHub.