When Brandon Bass tipped home a Paul Pierce jumper with 1:28 left in their 112-100 loss to the Spurs, the Celtics avoided joining San Antonio as the only other team in the last 25 years not to grab an offensive rebound. Instead, they grabbed one — an NBA statistic that’s occurred just 16 times in the past quarter-century.

Of course, three of those 16 occurrences now belong to the Celtics. Only the other two games produced an entirely different result: a 103-79 blowout of the 76ers this past April and a 122-103 defeat of the Pacers during the 2008 championship season. The C’s shot better than 50 percent on both occasions, just as they did in Wednesday night’s loss to the Spurs, so there weren’t exactly a lot of offensive rebounds to be grabbed.

In other words, the Celtics should hope they only have one offensive rebound every night.

“You’re a big believer in offensive rebounds I think; I’m not,” said Celtics coach Doc Rivers. “You can pick on that all you want. That is a number I rarely look at. Statistically, it holds up. I can tell you: You don’t offensive rebound, you stop transition, you win more games than when you get offensive rebounds. I can guarantee you that.”

Sounds great in theory, except for the fact that MySynergySports.com ranks the C’s rank dead last statistically in transition defense, which is a entirely different problem. And a much bigger one.

“Obviously, we would like to get some offensive rebounds, and if we’re under there we’ll take them,” added Rivers. “We didn’t get any, but that isn’t why we lost. Let me just say that. Offensive rebounds is the least of our problems.”

Overall, the C’s defensive rating (106.3 points allowed per 100 possessions) ranks them behind 21 other teams. Since Kevin Garnett‘s arrival, the Celtics have never finished worse than fifth in that category, and they’ve finished either first or second in four of his five full seasons, including tops in the league last season.

“You notice that we’re getting beat [on the glass], but what you don’t know is that we do a lot of helping,” said Garnett. “Our bigs do a lot to help our guards out. We strategically have different schemes that we throw at teams night in and night out, and where we get hit is offensive rebounding. It’s one of our flaws. That’s what it is, but we’re help a team, and that’s what we are. I don’t think Doc’s going to change that. …

“We’re not going to be able to take everything away. I’m sure some of the personnel that we’ve brought in for this year and some of the personnel from the past two or three years have been just for that, and it’s what we are. We’ll get better, and as the year goes on, I have a lot of confidence that we will get better.”

Only the Celtics haven’t shown any signs that it’s about to get better anytime soon. Against the Spurs, they allowed 100 points for the fifth time this season, including the third time in the last four games. San Antonio shot 58.4 percent from the field — also the fifth time the C’s have allowed an opponent to shoot better than 50 percent.

“We’re not taking away anything,” said Celtics point guard Rajon Rondo. “We gave up the corner 3 tonight, we gave up paint touches and paint finishes, we gave up too many and-1’s again. I think we probably lead the league in and-1’s, so we’ve got to do a better job — not to hurt anyone — but not let guys finish at the rim.”

Time after time, the Celtics remind anyone who will listen that it takes time to adapt new players like Jeff Green, Jason Terry and Jared Sullinger into their “grind-it-out” defensive identity, but nobody has an answer for how long that might actually take.

“That’s not who we are,” said Celtics captain Paul Pierce. “For us to do damage here in the Eastern Conference, that’s the type of team we’ve got to beat. It’s got to come from everybody. We’ve got to all look at each other in the mirror. It’s not just one particular person. It’s the starters starting out, it’s the guys on the bench. It’s a team game, so we’ve got to take it personal as a team and go out there and do something about it.

“When you have one breakdown on the defensive end, it breaks down all five guys. If you allow the ball to get to the middle, it’s like a domino effect. You have another man help and another man help, and it leads to wide open shooters or breakdowns on the defense. So, it has to come from all of us, where we’re always on the same page, communicating, talking, so those are the little things you have to do to be a great defensive team.”

If things don’t change, the Celtics might have to face an identity crisis before time runs out.