BOSTON -- Numerous hallmarks of Boston's success over the past two seasons have re-emerged over the past two weeks, but one area remains noticeably absent: third-quarter dominance.
The same scenario played out repeatedly during the 2007-08 championship season. An opponent hung close with the Celtics in the first half, then Boston shifted to another gear in the third quarter and motored away for a lopsided win that typically featured the starters on the bench in the fourth, laughing it up as the Gino video played on the scoreboard.
Now it's a luxury if the starters are lounging in the fourth quarter. They did so Sunday night against the Spurs, but only because San Antonio's dominance in the third frame helped the visitors turn this one into a different sort of laugher with a 94-73 triumph at TD Garden.
The Celtics trailed by a point coming out of intermission, but San Antonio scored the first 12 points of the second half while motoring away. The Spurs' lead ballooned as high as 17 in the third quarter and 25 in the fourth.
"I thought they came out with more of a sense of urgency in the third quarter," lamented Celtics captain Paul Pierce. "The extra-effort plays. It was a one-point game at the half and we just didn't make the second and third rotations. They were driving, being more of the aggressor, and they had us on our heels pretty much all of the second half.
"Like I said, they made the extra-effort plays tonight that we usually make. The team that you saw, San Antonio, the way they played is usually the way we play and we just got an old-fashioned butt-whupping."
Boston connected on 5-of-17 shots (29.4 percent) in the third quarter and was outscored 33-17. The Spurs generated assists on seven of their 13 buckets, suggesting the extra pass left Boston scrambling to cover.
"The third quarter was awful for us," said Rivers. "I thought the third quarter was when we stopped moving the ball offensively. And defensively, we struggled all night. [Manu] Ginobili was fantastic and [DeJuan] Blair in the fourth quarter was a one-man wrecking crew."
Rivers suggested the Celtics simply didn't have it in the third quarter Sunday, but the problem seems to run deeper.
Even in recent wins, Boston has allowed teams to hang around or rally in the second half, making things far more difficult than it sometimes needs to be (see Friday's win over the Kings).
The Celtics have scored in the teens in the third quarter of three of their last four games, and haven't topped 26 points in the third quarter since March 12 vs. Indiana (31). Twenty times this season the Celtics have scored 19 points or fewer in the third quarter.
"We just didn't play well," said Rivers. "Energy? I don't know. If you want me to say we didn't have energy, we didn't have energy."
And therein lies the troubling part. No one can explain why the Celtics have struggled out of the gates in the second half. They've been up and down, but rarely have they shown consistent play in the third quarter.
"I haven't been here, so I don't know about the past," said Michael Finley, who didn't get off the bench in the third. "I just know that tonight, offensively, we weren't scoring and, defensively, we weren't stopping them in the third quarter. When you've got those two things going against you against a good team, that's always going to make for a long night."
Boston generated a mere three assists in the third quarter, which Rivers chalked up to the fact that the ball became stagnant when shots didn't fall early on. As Finley noted, the offensive struggles led to frustration on the defensive end, and that's been a dangerous combination for Boston.
No Celtics player made more than one field goal in the third quarter. Pierce scored eight points with help of six free throws, but the most noteworthy aspect of his third quarter came when he crashed to the ground clutching his right shoulder after colliding with Ginobili while attempting a shot in the lane.
Pierce picked himself up, but the Celtics never did.
"I think the start of the third quarter kind of tore the game away," said Shelden Williams. "We kind of got robotic in the second half and couldn't come back."
The Celtics used to be robotic in the third quarter, in a good way. That's no longer the case. And of all the trademarks this team needs in order to maintain a championship level, third-quarter competitiveness could be the most important.
Chris Forsberg is the Celtics reporter for ESPNBoston.com. Follow him on Twitter. ESPNBoston basketball columnist Peter May contributed to this report.