For much of their N.B.A. play-in game against the Cleveland Cavaliers on Tuesday night, the Nets looked like the fearsome team that many observers had long said lay hidden behind their mediocre record. Kevin Durant was magnificent. Kyrie Irving didn’t miss a shot until the fourth quarter. Multiple teammates made significant contributions well above what was usually expected of them.

And yet, the game still came down to the final minutes after Cleveland, which had trailed by 20 points after the first quarter and then by 22 in the third, cut its deficit to 6 with a just over a minute left.

The job got done in the end: The Nets pulled out a 115-108 victory to claim the No. 7 seed in the Eastern Conference, and a matchup with the Boston Celtics in the first round. But the game was the latest example of a Nets performance that could be quantified as a head-scratching mix world-beating talent and worrisome lethargy.

For the glass-half-full crowd, the Nets stars Irving and Durant combined for 59 points on 31 shots while handing out 23 assists, another stat-sheet-filling display from one of the most talented tandems in the N.B.A. It was, again, a tantalizing glimpse into what their partnership could be at its peak — a summit that has been a rare sighting in their time together in Brooklyn.

But it wasn’t just them. Bruce Brown, the team’s consummate role player, had 18 points, 9 rebounds and 8 assists, often offering himself as a crucial release valve on offense when Durant and Irving would get blitzed by defenders. Andre Drummond punished Cleveland on the boards, scoring 16 points and grabbing 8 rebounds in only 19 minutes. Nic Claxton, the spry reserve center, added 13 points, 9 rebounds and 5 blocks off the bench.

But the glass-half-empty set had evidence, too, after the Nets nearly blew yet another lead down the stretch against a lesser team. On Sunday at home against the Indiana Pacers, one of the worst teams in the N.B.A., the Nets endured a similar ending that became uncomfortably close. In the game before that — also against Cleveland — the Nets blew a double digit third-quarter lead. Before that was a game against the Knicks, another less talented team playing out the string; the Nets trailed by 21 points in the first half that time.

All three of those games required fourth-quarter rallies to win, but all three repeated a pattern that has played out for much of the season: The Nets, while supremely talented in a couple of spots, are a squad that struggles to put together wire-to-wire performances. And in the playoffs, against the best teams in the league, that may be their Achilles’ heel.

“That’s a part of our journey too,” Nets Coach Steve Nash said Tuesday of trying to find a way to change his team’s penchant for flirting with disaster. “It’s not just go out there and build 20-point leads. Turn it into 30.”

In the opening game of their first-round series on Sunday, the Nets will travel to Boston and find a Celtics squad that is not the same team the Nets easily dispatched last season. And, thanks to the Nets’ Brown, the Celtics now will have some bulletin board material as motivation.

Asked about the Celtics on Tuesday, Brown suggested the absence of Robert Williams III, Boston’s starting center and one of the league’s best defenders, would mean that “they have less of a presence in the paint.”

The comments did not sit well with Durant, who dismissed them as “caffeine pride talking.” Brown had said that, with Williams out, the Nets “could attack” Boston’s Al Horford and Daniel Theis.” referring to Horford and Daniel Theis, who round out the Celtics big man rotation. Durant grimaced and noted, “Them two dudes can do the same stuff.”

Durant’s fitness is another lingering concern for the Nets entering the Celtics series. Just getting into the play-in tournament required a heavy workload for Durant, who played 42 minutes on Tuesday night. Since the All-Star break, Durant has averaged 38.6 minutes a game. While other stars around the league were able to manage their minutes — and save their legs — during the stretch run, the 33-year-old Durant had to expend more energy than usual just to drag his team into the playoffs.

One way or another, the Nets will enter the playoffs much as they did last season: With high expectations and little time together. Last year, that was a result of injuries and a trade for James Harden. This year, it is a result of injuries and the decision to trade Harden away (not to mention Irving’s extended absence over his refusal to be vaccinated against the coronavirus).

“We’re just such a new group,” Nash said. “I think that was like the seventh game those nine players tonight have played together. So every day is a day for us to learn about ourselves

All season, though, the Nets have bet that talent trumps cohesion. It is why they shuffled players in and out of the rotation with frequency, why they were willing to trade Harden. Tuesday night’s victory showed a tease of the championship potential in the group.

In the first three quarters, anyway.