It wasn’t a polished or impressive effort by the Celtics on Wednesday night against the Denver Nuggets. It was, however, a mature one.

The Celtics have endured a topsy-turvy first half of the season because they have been playing to the level of their opponents. Just a month ago, the Celtics were 18-13 with a game against the Lakers, two against the Nets, and a home contest with the Pistons upcoming.

Boston lost three of those four games, including an inexcusable home loss to the Lakers. That sent the team on a downturn with them crashing to a .500 record.

After back-to-back 20-plus-point wins over the 76ers and Wizards, the Celtics entered a soft portion of their schedule, beginning with the Nuggets followed by back-to-back contests with the Magic, and then a road game against the Knicks.

It seemed the Celtics felt they would glide through that late-December schedule because of superior talent, and they paid for their arrogance. That was not the case Wednesday. The Celtics punched the Nuggets in the mouth, maintained the pressure, and then staved off a late run after taking a 22-point lead.

The 111-103 win was a sign of maturity for a team that now realizes it can compete for the second seed in the Eastern Conference. Following Wednesday’s play, the Celtics were just a game behind third-seeded Atlanta in what is expected to be a thrilling race.

There are 13 teams with legitimate chances at the eight playoff spots, and only seven games separate seeds 3 and 13. So, that makes drab games such as Wednesday’s important. The Nuggets have talent. They are athletic and are one of the four teams that have beaten the Warriors this season.

The Celtics couldn’t take this victory for granted, and they didn’t.

“We don’t have any room to really [play down to the level of our opponent],’’ swingman Evan Turner said. “Every game is always important to us and we’re trying to build and be better and play to our standards. We can’t do what a lot of teams do, like take a break before the All-Star break.

“Everybody’s bunched up. You lose two games and you’ll be back in the eighth or ninth seed. It’s bad luck to count your money before you’re done gambling. We’re not too much worried about the second or third seed or whatever.’’

As Turner loosely quoted Kenny Rogers, he made an astute point. The Celtics are hardly talented enough to take games for granted. They didn’t on Sunday against the 76ers, a team that has played better following the addition of point guard Ish Smith. The Celtics jumped out to an 18-7 lead and never trailed.

On Monday, the Wizards were a team looking for blood after losing to Boston three previous times. After taking the lead late in the second quarter, the Celtics continued to play with passion and extended their lead to the point where Jonas Jerebko was dunking on Kelly Oubre in garbage time.

And they didn’t take the Nuggets lightly. Denver’s last lead was 5-4 with 9:04 left in the first quarter. The Celtics played well with their shortened rotations, Avery Bradley getting off to a hot start and Kelly Olynyk continuing his improved play.

They responded with an 18-1 run after the Nuggets sliced the Celtics’ lead to 75-70. And when the Nuggets made one final surge late in the fourth quarter, Isaiah Thomas, likely headed to his first All-Star Game next month in Toronto, and Jae Crowder stabilized matters.

It was a satisfying victory because the Celtics avoided disaster. They need to win the games they are supposed to win. With just 35 games left in the regular season, they need to shake their erratic tag.

“I think we are more focused on ourselves, mainly when teams start to lock in they start to break down where we are at in the East and with the Western teams,’’ center Amir Johnson said. “We definitely need to focus on every game and know that every game counts for us. It is just a complete focus for us. Coming up on the All-Star break we want to try and get every game.’’

It seems the Celtics have finally realized they have the potential to be one of the more talented teams in the Eastern Conference. The key is playing to that level on a nightly basis, even when they are not as sharp. The Celtics shot just 42.7 percent and missed 19 3-point attempts.

They struggled at times with Denver’s mammoth center duo of Nikola Jokic and Jusuf Nurkic, and did slip in the fourth quarter when Denver attacked the basket.

But the game was never truly in doubt following that 18-1 run, and the Celtics cleared an important hurdle on their way to appreciating prosperity. That’s the sign of a maturing team.

Gary Washburn can be reached at gwashburn@globe.com. Follow him on Twitter @GwashburnGlobe.