DENVER — After struggling throughout December, the Celtics were hit with perhaps their toughest test of the season in the form of their four-game trip. They bounced around different Western Conference cities, facing formidable foes all vying for playoff positioning.

The end result: a 3-1 record as the Celtics return to Boston. But, naturally, the reigning champs aren’t satisfied with the entire trip. There were bright moments, yes, but they still dropped that disappointing Thunder game.

“It was supposed to be 4-0, but the second-best was 3-1,” Celtics coach Joe Mazzulla said. “Everybody said this road trip was brutal, I think, was what a couple people used to start. So that was great. I just liked the way our guys handled it. I liked the way we approached it. It was four tough environments and I thought our defense kind of carried us and I thought our offense was what helped us.”

As Mazzulla pointed out, the Celtics’ defense flashed its teeth to open the New Year. The latest result was a 118-106 win over a Nuggets team missing Nikola Jokic. Even in the Thunder loss, the defense kept them in the game before the offense’s struggles were too much to overcome. The Celtics are 27-10 on the season, the third-best record in the league.

There are reasons for optimism, too, as the Celtics are finally healthy. They were supposed to be at full strength in Denver, though Derrick White was a late scratch due to an illness. Regardless, the Celtics don’t have any lingering injuries — they can finally deploy their full roster with all its might.

“I don’t think we were excellent but I think we’re getting (close),” Kristaps Porzingis said. “I think we’re going to turn the corner and go on a nice run. I really believe so. … We’ve had two games with a full roster this season. So obviously it’s tough. And then also me coming back and getting back in shape, it’s not easy for guys. But now we’ll get some consistency now I believe.”

The Celtics are still a work-in-progress even though they brought back virtually their same roster from the title-winning team. Missing Porzingis for stretches of the season has affected their cohesiveness. Most of the starters have had injuries or absences forcing them to miss a handful of games.

Following that trip, the Celtics get some rest. They play just three games in nine days, all against teams under the .500 mark. But then the schedule picks up with nine games in 15 days, which features two back-to-backs and another four-game trip out West. For now, the Celtics aren’t worried about that as they look to continue improving their game.

“3-1 is pretty good,” Jayson Tatum said. “We wanted to win every game. We wanted to be 4-0. Sunday was tough but we bounced back and responded tonight. And we’ll just go back home and continue to build off this game and keep it going.”