After the Celtics defeated the Bobcats, earning their sixth straight victory, the generally jovial Jason Terry walked through the locker room, head down, repeating: “Tough game. Tough game.”

He had just finished the worst night of his Celtics career, a scoreless effort in 15 minutes. Heck, C’s coach Doc Rivers even played Leandro Barbosa over Terry in an eight-point game midway through the fourth quarter.

“Just a feel, honestly,” said Rivers. “I thought we needed energy, and he’s always ready.”

Energy? Terry’s made a living on energy, finishing among the top Sixth Man of the Year candidates for as long as some of his teammates have been in the NBA. Yet, on a Monday night against the Charlotte Bobcats in the middle of January, he couldn’t get on the floor. For the time being, the tides have turned against Terry.

In November and December, Terry didn’t entirely meet the expectations set by his three-year, $15 million deal, but at least he averaged double-digit scoring on near 40 percent 3-point shooting in 30 minutes a night. That was only supposed to improve once Avery Bradley returned and allowed Terry to find his comfort zone off the bench.

Instead, he’s played 16 or fewer minutes in three of the C’s seven games this month, including a combined 31 minutes over the past two games. In the seven games since Bradley’s return from shoulder surgeries, Terry’s averaging only 4.6 points on 34.9 percent shooting from the field (23.8 3-point percentage).

Courtney Lee, who struggled mightily to start the season, appeared to be the odd man out. In the game prior to Bradley’s return, Terry dropped 20 points for the first time all season while Lee went scoreless in 21 minutes, and that was a microcosm of what the Celtics had seen from them all season.

Yet, once Bradley joined the starting lineup, the C’s rediscovered an identity forged by defense. Even Terry admits he’s not known for his defense, but Lee feeds off Bradley’s energy. He picks up where the young lockdown defender leaves off, providing relentless pressure on opposing backcourts.

“If you really want to get deep,” said Lee, who finished with nine points (4-7 FG) in 17 minutes, “I’ll take it back to just life, period. I didn’t have the best childhood, I continued to fight, and you use that same philosophy on the court. Something might not be going right, but you can always give effort. Effort takes no talent.”

That effort led to the Bobcats backcourt shooting a combined 37 percent on a whopping 49 shots. It’s also translated into a 6-1 record since Jan. 2, coinciding with Bradley’s return and Terry’s cold streak. As a result, it might not be so easy for Terry to regain minutes on what Lee calls “the deepest team that I’ve been on 1-12.”

“Defense is going to lead to offense,” said Lee, whose shooting better than 40 percent from 3 this month. “Once you get in a rhythm on defense, you’re definitely going to have one on the offensive end.”

Only, Terry’s always taken the opposite approach, and at 35 years old he’s not likely to find a new identity.