BOSTON -- All season long, the Celtics have struggled in late-and-close situations. And, all season long, Jayson Tatum has struggled to make jump shots.

Both trends converged here at TD Garden Friday night to send the struggling Celtics to one of their most disappointing losses in a season featuring more than a few to choose from.

Tatum's missed 3-pointer with 6.7 seconds remaining was one of nine straight misses Boston had over the final 7 minutes 19 seconds of its 109-105 loss to the Portland Trail Blazers, allowing the visitors to close the game with a 20-5 to snatch a victory that it appeared the Celtics had well in hand.

"It hurts," said Tatum, who finished with 27 points, 10 rebounds and seven assists in 41 minutes, but missed all six of his 3-point attempts. "It bothers you, as it should. But you can't go back in time.

"It's just get back in the gym, watch some film, learn from your mistakes, and try to improve on them."

While Tatum did plenty of other things right -- for much of the second and fourth quarters he served as the team's de facto point guard, with starter Dennis Schroder anchored to the bench, and was able to repeatedly gash Portland's defense to either score at the basket or get fouled, as he racked up 14 free throws -- the missed shots once again stood out.

Tatum's six misses from beyond the arc Friday night extended his streak of consecutive missed 3s to 20 -- a career-high -- while his 0-for-17 mark across the last three games is now the second-most in NBA history, behind only guard Michael Adams, who went 0-for-18 over a three-game span 30 years ago.

And while Tatum hasn't been that cold over the course of the season, it does continue what has become a season-long slump for him as a shooter. Including Friday night's loss, Tatum's effective field goal percentage on jump shots is now 6.9 points below what it is expected to be, per Second Spectrum's tracking data -- a gap that ranks last among 67 NBA players who have taken at least 300 jump shots.

Essentially, that makes Tatum the unluckiest jump shooter in the league.

Meanwhile, when isolated to just 3-point attempts, Tatum ranks 75th out of 79 players in the same metric who have attempted at least 200 3s. And, as a team, Boston ranks 29th out of 30 NBA teams in the same category.

But while saying Tatum and the Celtics have been unlucky with their shooting this season offers an explanation for what's happening, it doesn't change the fact that the shots, ultimately, aren't going in.

"I don't know," said Tatum, who is now shooting 31.1 percent from 3-point range after entering this season a 39.6 percent shooter from deep, when asked if there's anything he can see that's causing him to struggle to shoot the ball the way he has been this season. "Maybe stuff like this happens every once in a while.

"But I know for myself, and I guess some of the other guys who aren't shooting as well, it's not going to change how people guard us. They know what [I am] capable of, and it's just a matter of getting out of it.

"And I will, and we'll be able to talk about something else."

It would've helped change the conversation around Tatum's night Friday if Boston hadn't gone cold as a team down the stretch -- another common theme to Boston's season. The Celtics are now 9-17 in clutch games this season (ones with the score within 5 or fewer points inside the final five minutes), which ranks 27th in the NBA -- just as they did last year.

Not all late-game collapses are made equal, however, and this one was particularly painful. After Boston (23-24) took a 100-89 lead on a Grant Williams layup with 7 minutes 19 seconds remaining, the Celtics didn't make another shot the rest of the game. In fact, they didn't score for nearly seven minutes, until making a handful of free throws inside the final minute as the two teams traded the lead back-and-forth.

Portland (19-26), meanwhile, kept chipping away at Boston's lead, and after taking the lead with 31.6 seconds to go on a Robert Covington 3-pointer in the corner -- his first make of the game, which came after Jaylen Brown left him to double into the post -- Jusuf Nurkic, who finished with 29 points, 17 rebounds and six assists (all of which led the Blazers), flipped in a putback of an Anfernee Simons miss that proved to be the game-winning shot.

"It's a little disappointing because we had been better in those situations execution-wise," Celtics coach Ime Udoka said. "And, at times, as simple as it sounds, it comes down to making some open shots.

"And they dared some guys to make and took it out of [Tatum's] hands, and we didn't didn't make them pay."

The loss drops Boston back under .500 on the season, and to 59-60 going back to the beginning of the 2020-21 campaign. That's a long period of time where the Celtics have been a .500 team despite having two of the best young wing players in the league in their employ.

But both Tatum and Udoka said they believe Boston is capable of more than that -- if the Celtics can find the consistency that's eluded them so far this season.

"We do have to be more consistent," Udoka said. "We had some really good wins and some good games overall lately. When you look back at our last 15 or so of where our net ranking is offensively and defensively. We've been progressing the right way, so that's why this one does sting more than the others. I felt like we had learned from those early season situations and have to stay consistent as far as that [goes]."