DENVER — The road has favored the Celtics as they enter 2025, and they return home with winning records after a successful sweep of four Western Conference teams, one bad quarter shy of an undefeated trip.

The growth is evident, particularly on defense, where the Celtics have been energetic, determined and impactful during this stretch, including Tuesday’s travel finale, a 118-106 victory over the undermanned Denver Nuggets at Ball Arena.

Denver was missing three-time MVP Nikola Jokic, who tried to warm up hours before the game began but was sent home due to illness. Undermanned teams have thrived against the Celtics in recent years, so the schedule has been adjusted. Denver was without the league’s most versatile player, so Boston focused on keeping Jamal Murray in check, sending two defenders on him on nearly every possession in the second half and playing with the urgency to match.

The Celtics needed this win, especially since they were beaten in the final period in Oklahoma City on Sunday and wanted to avoid a losing streak. The stakes rise for Boston as the calendar turns to January. it is approaching mid-season. Oklahoma City and Cleveland are trying to create distance from the rest of the field, and the Celtics need to start asserting themselves as they prepare for another long playoff run.

Defense comes first. And their emphasis on this team over the last four games has been impressive. Of course, the Celtics’ focus on Murray meant that other Nuggets got a chance to thrive, and they did, but eventually the defense made an impact.

“With Jokic out, I understand how important Murray is to the game,” Celtics coach Joe Mazzulla said. “The fact that he doesn’t want to have a lot of influence has a lot to do with it. For most of the game we were very careful to shift the player around and have him play against multiple defenders in a scrum. And we can withstand some (above average) shots from those (other) guys, but it’s something you have to live with.”

Murray scored four points in the second half and the Celtics let Russell Westbrook cocoon himself for his days in Oklahoma City with 26 points, but he also committed eight turnovers and was minus-13. The Celtics played a smart game, knowing that her talent and strength would prevail in the end. It’s an encouraging sign.

Although this Celtics team has a championship under its belt and has several experienced players who have been through playoff wars, it is far from a finished product. You need to make improvements. Last week was a big step forward.

“Everyone said this road trip was ‘brutal,’ I think a few people did,” Mazzulla said. “It was great. I like the way our guys handled it. I like the way we approached it. There were four difficult situations and I thought our defense kind of carried us and our offense helped us.”

Mazzulla shifted his approach to the intangibles.

“I really like the road trip mentality they brought,” he said. “The physicality they needed was there in all four games. The connectivity. I think we became a better team on this road trip. We just have to keep it that way.”

The Celtics allowed 103 points per game during that trip, shot nearly 47 percent from the field and thrived in the other key categories Mazzulla highlights. Without that brutal second-half offensive performance against the Thunder, the Celtics would have come home unscathed. But the trip was still successful.

“Every game offers a different lesson and (Tuesday) it was the ability to understand each other and play for each other on offense,” Mazzulla said. “And continue our physicality defensively. The last game was about getting to know each other and learning how we need to respect each other’s space and be better on offense. In the Houston game I thought we answered the call physically, and in the Minnesota game we played a great defensive team that gave us problems in a couple of close games.

“I think when you go on certain road trips like this, you can get better as a team on and off the field. I thought we did it.”

The key to the Celtics moving forward is to stay healthy, integrate Kristaps Porzingis better, play more consistently and continue to improve defensively as the competition intensifies. But there was a sense of uncertainty as the Celtics embarked on this four-game trip. They had just been beaten at home by Philadelphia and Indiana before facing inferior Toronto.

They proved they were up for the challenge, especially on Tuesday, when the Nuggets made a plethora of difficult shots and actually tied the game at 93 with eight minutes left before the Celtics cemented the win with a 15-0 run , with Jayson Tatum (29 points) scoring the last two buckets. They were tough enough to withstand the Nuggets’ attack and smart enough to outlast an inferior opponent.

“I mean, 3-1 is pretty good,” forward Jayson Tatum said. “We wanted to win every game. We wanted to be 4-0. Sunday was tough, but we recovered and responded (Tuesday). Just go home and keep growing this game.”

Gary Washburn is a Globe columnist. He can be reached at [email protected]. Follow him @GwashburnGlobe.