The Nuggets’ Saturday night matchup against the Pelicans was supposed to be about new beginnings and an opening night starting lineup walking to the center circle together for the game’s opening tip for the first time since Oct. 20, Denver’s second regular season game.

Instead, the Nuggets unearthed an old habit: relaxing on defense when their offense is clicking. At least that’s what Mason Plumlee identified after the game as one of the main factors that contributed to the Nuggets’ worst loss of the season, a 120-112 defeat at the hands of the Anthony Davis-less Pelicans.

“We were up by 19?” Plumlee asked, almost dumbfounded to learn the Nuggets were leading by that many points in the second quarter. “I think the game became easy on offense, so we stopped playing defense.

“I think that’s definitely shown up in some of our losses,” Plumlee continued. “I think you’ve just got to address it. We’ve won some games with our defense, but we can’t just rely on the offense.”

Mental lapses, a lack of aggression on the defensive end of the floor, not enough discipline: all of Denver’s defensive foibles were on display tonight as the Pelicans flew back from a 49-30 second-quarter deficit. Denver and its opening night starting lineup got out to an early 11-3 lead, stretched its advantage to 12 after the first quarter and led by 19 in the second. Then, Julius Randle (28 points and 10 rebounds) and Jrue Holiday (29 points and five assists) took over.

But it was another mid-to-late second quarter debacle again that did Denver in. After leading the Jazz by three points heading to the second earlier this week, the Nuggets found themselves down by 15 points as the two teams walked to their respective locker rooms. Forty-eight hours later, Denver led 39-27 after 12 minutes of play but was outscored 40-32 in the fateful second period. The Nuggets scored a healthy 32 points in the second quarter but it came on just 10-24 (42 percent shooting).

“I think we start off the game with the right intentions, with the right mindset,” said Paul Millsap. “I think these last two games in first quarters I think we’re pretty good. Second quarters really hurt us in both games. We’ve just got to figure that out. Whatever reason it is, it’s something we’ve got to figure out. But it’s all part of the season. Things happen.”

For one, whatever lead that’s presented to Denver’s bench quickly evaporates.

In his sixth game in a Nuggets uniform, Isaiah Thomas struggled mightily. He scored 12 points but needed 14 shots to reach that total and failed to register an assist in 16 minutes of action. When Thomas subbed off in the fourth quarter for good, he had attempted a team-high 14 shots. Denver was outscored by four points while he was on the floor, but more alarmingly, the unpredictable free-flowing offense, which had been a staple of the Nuggets’ bench for the entire season, has vanished as of late.

“Probably a little more pick and roll than usual, early in the shot clock too,” Plumlee said regarding Denver’s second unit offense. “What makes us good is our movement and our flow, less play calls and whether its pin-downs, flairs, stuff off the ball. So I know that will be a point of emphasis for me going into next game playing as a screener.

“Not intentionally, but there definitely has been,” Plumlee added when asked if he’s noticed that shift take place over the last few games. “Our bench has been a big part of what we do, so it’s got to get back to what it was.”

Nuggets coach Michael Malone was critical of his second unit’s play earlier this week and hinted that he’d tweak his bench lineups following Denver’s loss to Utah. He did, but it’s still apparent that the Nuggets’ second unit isn’t fixed as that group’s problems have come to a head over the last two games. Thomas was expected to have coats of rust from his 11-month layoff that would only be washed off by game reps, and he has, but the former MVP candidate hasn’t been the plug-and-play option at point guard that some around the team thought he’d be right away.

Monte Morris, who labeled Denver’s second unit offense as “stagnant” on Thursday, could have spoken for the entire Nuggets locker room. Will Barton echoed Morris’ thoughts that night, and after falling at home for the second time this week — more times than the Nuggets did from Nov. 13 to Jan. 15 — Plumlee was singing the same tune. Malone and his players know why their bench, which played so well for the entire season, is running into trouble. What are they going to do to fix it?

Of course, there were other contributing factors to this Nuggets loss. Denver’s starters didn’t play particularly well either. Nikola Jokic was plagued by foul trouble for a second consecutive game and only played 22 minutes. He did post an impressive 10-points, nine-rebound, seven-assist line, however. Jamal Murray shot an inefficient 5-15 from the field. Gary Harris was quiet, failing to crack double-figure scoring. Barton had an off night on the offensive end of the floor too, finishing with only eight points on 3-11 shooting after back-to-back 20-plus outings. Denver probably rolls if Jokic plays close to 30 minutes.

After shooting 7-19 from three in the first half, the Nuggets went as cold as the blizzard that dumped six inches of powder on the city Saturday night. Denver hit only two of its 13 triples in the second and third quarters.

“It’s something that’s uncharacteristic of us, trying to get it all back at once,” said Millsap. “We were trying to play hero ball a little bit, but intentions were good. Guys were out there trying to play, trying to fight. Things just didn’t go our way.”

The second unit’s struggles are a first-world problem for the Nuggets. Denver is still flying high at second in the West, a full four games up on the Oklahoma City Thunder with 20 games remaining. The Nuggets have the inside track on the No. 2 spot in their conference by virtue of the head-to-head tiebreaker they hold with the Thunder and the odds are that’s where they’ll finish the regular season.

But before then, Denver has to figure out a solution to its bench rotation. The Nuggets have been outscored by 13 points in Thomas’ 51 total minutes this season and over Denver’s last three games, Thomas is a minus-22 in 42 minutes. Morris, who should be a candidate for Sixth Man of the Year, hasn’t played more than 20 minutes in three-straight games and is getting frozen out of Denver’s attack when he and Thomas share the floor. He needs the ball in his hands more.

Based on the transparent comments that have filtered out of the Nuggets’ locker room over the last few days, Denver knows why its bench unit is running aground.

Now, something’s got to give.