When they crushed the Golden State Warriors 140-88 at the start of this month, the Boston Celtics simultaneously exorcised some of the ghosts of the 2022 NBA finals and added further lustre to what is on course to be a historically high-achieving regular-season campaign.

Thanks to 29 points from Jaylen Brown and 27 from Jayson Tatum on his 26th birthday, it was the third-highest margin of victory in Celtics history and their third 50-point win of the season – an NBA record. It was also their 11th win in a row, a run during which they had demolished their opponents by an average of 22 points, a margin of victory unmatched in NBA history over a single-season winning run of 10 or more games.

Boston’s record improved to 48-12 with the victory, and they held Stephen Curry to just four points in a win so dominant that Golden State coach Steve Kerr benched his starters for the entire second half after the Celtics had raced to a 44-point half-time lead.

“That’s what we used to do to teams,” Curry said after the game.

But as quickly as the Celtics had asserted their championship credentials against the Warriors, defeats in their next two games showcased many of the issues that have seen recent playoff runs end short of a title.

First, in what Brown termed “a mentality loss”, they let slip a 22-point fourth-quarter lead to lose 105-104 to the Cleveland Cavaliers on Tuesday night. It was a loss that could have been written off as a blip in a busy schedule were it not for the fact that it was yet another example of Boston’s struggles with late-game execution.

One of the biggest criticisms of the Celtics in the postseason over the last two years has been how their play slows late in close games. The Celtics haven’t been involved in many truly close contests this season, but when they have, the same old problems have returned. Taking the season as a whole, Boston rank 18th in the league when it comes to pace – defined as the average number of plays per 48 minutes. In clutch scenarios – the final five minutes of the fourth quarter or overtime when the score is within five points – the Celtics’ pace ranks 30th.

With the game on the line against the Cavaliers, head coach Joe Mazzulla elected not to call a timeout to draw up a designed play – another common criticism of the Celtics in the playoffs. Instead, the Celtics put the ball in the hands of their best player, Tatum, and let him work. But this resulted in the All-NBA forward dribbling down the clock and launching a low-percentage and ultimately unsuccessful fall-away jump shot.

Two days later, the Celtics performed better in the fourth quarter, outscoring the Nuggets 29-25 in the final period in Denver. It was not enough to overcome the reigning champions, though. And the most glaring reason for that defeat was again an issue they have bumped up against in the playoffs – against the very best teams, they rarely have the best player on the court.

Tatum shot a miserly five of 15 from the field against the Nuggets. He had as many turnovers as made field goals. Nikola Jokic, Denver’s two-time MVP, had 32 points, 12 rebounds and 11 assists on a hyper-efficient 59.7% shooting.

As the Celtics rallied late in the game, Tatum missed an open corner three-pointer that would have given them the lead inside the final minute. It was another example of his struggles in the clutch. Tatum is averaging just 2.5 points in clutch minutes this season and shooting 31.1% on field goals. In contrast, Jokic is averaging 3.6 points in clutch time on 54.8% shooting.

Of course, Tatum is yet to reach his peak. He is only 26 years old. At worst, he is already one of the 10 best players in the world. He has delivered in high-pressure postseason moments in the past, too, including a 46-point performance in an elimination playoff game against the Milwaukee Bucks in 2022 and a Game 7 record 51 points against the Philadelphia 76ers in last season’s Conference semi-finals.

Tatum’s case to be named this season’s MVP all but ended last week after the defeats to the Cavs and Nuggets. He lamented the fact he feels MVP voters mark him down for past postseason struggles, most notably his under-performance against the Warriors two years ago. He may have to lead Boston to a title, something he is capable of, before those doubts are erased. But in the last 30 years, only two teams have won the NBA title without a current or past MVP on their rosters – the 2004 Detroit Pistons and the 2019 Toronto Raptors, who in Kawhi Leonard boasted a former finals MVP. So often when it comes to the playoffs, the team with the best player prevails. At present, the Celtics can’t claim to have the best player when matched against their most likely late postseason opponents.

Tatum can’t do it alone and Boston still have arguably the most talent-packed roster in the league. Preseason additions Jrue Holiday and Kristaps Porzingis have added new dimensions on offense and defense. Porzingis, in particular, stands out: his scoring in the low post is a fresh string to Boston’s bow. Mazzulla should lean into the Latvian late in games, too, perhaps trusting the 7ft 3in center’s 66.7% clutch shooting when it comes to who takes the last shot in close games.

Boston bounced back impressively in Phoenix on Saturday, beating Kevin Durant and the Suns 117-107 to avoid what would have been the Celtics’ first three-game losing skid of the season. Tatum was back on form, too, scoring 29 points, in addition to 10 rebounds and seven assists – although he still shot a below-standard 39.2% from the field.

And even after their recent setbacks, the Celtics are still on pace to record one of the great regular-season campaigns of recent times. They have all but wrapped up top spot in the Eastern Conference, eight games ahead of the Milwaukee Bucks in second place. They rank first in the league in offensive rating and third in defensive rating. Their league-best average winning margin is the sixth-best in NBA history – all but one of the five teams ahead of them went on to win a championship the same season.

“That’s a really good team over there,” Tatum said after Thursday’s defeat in Denver. “Well coached. They make the right plays more often than not and you’ve got to beat them. You can’t depend on them to beat themselves.”

With that statement, Boston’s star player hit upon the biggest difference between his team and the reigning champions: if the Celtics are to have any hope of landing a first title since 2008, they must learn how to get out of their own way.