PHILADELPHIA — Isaiah Thomas is out for at least one more game, today against the 76ers, and until their dominant scorer returns, the Celtics have only one quality they can fall back on.

“Our team is built on tough guys with chips on their shoulders,” said coach Brad Stevens. “That’s been really important as we’ve been building in the last four years, is having an environment led by that mindset.”

That mindset is what kept the Celtics alive during their win Friday night over the Nets, at least until their offense finally caught a spark in the fourth quarter.

The C’s reconvened for practice yesterday at Temple University’s McGonigle Hall, and Marcus Smart gave a thought to that comment by Stevens.

“It counts a lot,” said Smart. “We have guys that have something to prove. When they’re on a mission they become real deadly. A lot of guys on this team have a lot to prove.”

They still have to prove it to themselves, too. Smart and others called out the team last fall for not defending up to last season’s standard, essentially saying they had become soft. He may be ready to admit the tough-guy standard is again being earned.

“We’re getting back there, definitely,” he said. “Some work to do, but there’s more and more games we’re playing that way, putting those types of games together. We see glimpses of it, but we have to do it for a whole 48 minutes.”

The Celtics were a bottom-five defensive team last fall, and as of yesterday had risen to 12th in the league in defensive rating. Other things may be beyond help. They’re 27th in rebound percentage.

But thanks especially to the return of Avery Bradley, the Celtics are clawing their way through defensive possessions. It’s how they’re built, according to Smart.

“I see it, just knowing Danny Ainge and the type of player he was, what he likes and how he likes to play,” said Smart. “I can definitely see that in the way this team was built.”

Smart has seen video of some of the C’s president of basketball operations’ old scraps, though everyone scrapped back then. He broke into a laugh at mention of Ainge’s legendary brawl with Tree Rollins.

“Danny likes players who like those types of things,” said Smart.

But, as Stevens stressed yesterday, the key to becoming this type of team again depends on what comes next.

“Never really felt the mindset wasn’t there. There’s a lot of factors of why you’re not defending at the best level,” he said. “One of the factors is availability, but sometimes you get Minnesota, the top defense in the league, and we come in and hit shots against them. Lot of factors, but we’ve been more consistent in what we need to do, and that’s the most important thing.

“We’ve played better recently and the numbers back that up,” said Stevens. “But that’s something you have to go do the next game. It’s hard to be a good defensive team night in and night out. The difference between a top-10 defensive team and whatever we are right now is a point per possession, maybe. One point out of a hundred possessions. So it’s a small margin. We just have to continue to build on what we’ve been doing, because we’re getting better.”

Celtics notes

Jae Crowder has had six double-digit rebound performances since the All-Star break, and is admittedly attempting to board more.

“A lot of guys thought we were going to bring in a rebounder, so I took it a little on myself to be more aware of the situation, try to help as much as possible,” said Crowder. “I knew I could get in there and get a few more rebounds . . . Help the bigs a little bit.”

Crowder’s 12 rebounds on Friday against Brooklyn was a nice underpinning for his nine-point fourth quarter, which included a pair of 3-pointers and a three-point play that gave the Celtics the lead for good.

“He’s a guy who can shoot, he’s figured out his best places to drive it, when he can post, scoring in a variety of ways depending on who is guarding him,” said Stevens. “He’s effective at the 3, he’s effective at the 4, and he’s versatile defensively. He’s hard to keep off the court because of all those things.”