Celtics coach Brad Stevens knows that seasons do not end in January, and playoff seeding is not decided then, either. So his hope, after his team lost on Saturday for the sixth time in eight games, is that this relatively mild funk will have value when more important moments arrive.

“This will be a good stretch when we look back on it, because it will force improvement,” he said after his team’s 123-119 loss to the Suns at TD Garden. “It’ll force urgency on every detail. It’ll force us to do our jobs for 48 minutes. These are never fun to go through. It sucks. But this is usually what you look back on and say it was a springboard for you.”


Nevertheless, right now Saturday’s loss to the 18-win Suns is probably a new low point for this year. The general themes remained familiar.

There was another slow start, this one resulting in a 16-point first-quarter deficit. There was another below-average opposing shooter getting open and pouring in 3-pointers, this time Mikal Bridges, who entered the night below 30 percent but made 6 of 8. And there was another roster that was hardly whole, this time with starters Kemba Walker (knee) and Jaylen Brown (thumb) watching in street clothes and leaving Stevens to keep fiddling with unusual rotations like they were combination locks.

Saturday’s loss wiped away a historic 3-point shooting effort by a player who has historically been one of the team’s worst 3-point shooters. Just nine seconds into the game, Marcus Smart hit a shot from beyond the arc, and he said he could tell then that plenty more would follow. In all, he made 11 of 22 threes, setting franchise records for attempts and makes. He also scored a career-high 37 points.

Smart kept shooting because he was in a groove, and because the absences of Walker and Brown meant that the shots had to come from someone. Of course he was pleased with his night, particularly given the disrespect he is generally shown as a shooter. He saw the Suns constantly go under screens set for him, and barked at their bench a couple times after making shots near it.


But he also found this record hollow. He is the most intense competitor on this team, and this losing is grating on him.

“Right now it means nothing,” Smart said. “I’d trade all that in for a win, especially with the way this team has been playing. I’d rather have the win than the record.”

After the loss, there was a lot of talk about how this rut has been ignited by Boston’s defensive slippage. And there is no question that it has been an issue, especially after allowing an average of 125.5 points over the last two games.

But the blemishes have been wide-ranging. Over the last eight games, Boston has the NBA’s 17th-ranked offense and 16th-ranked defense.

The players say that they are allowing slow starts on offense to seep into their defensive effort. Also, it’s considerably more challenging to catch an opposing team off guard when it has just scored and has time to set its defense. The personnel absences do not help, either.

“If you do all the right things, if one person has a little slip up,” Stevens said, “that’s hard for us.”


Bridges’s strong shooting surprised the Celtics a bit, but Devin Booker’s shouldn’t have. He is the same player who scored 70 points in a game here nearly three years ago. On Saturday, he made 12 of 20 shots and had 39 points, 10 rebounds, and 9 assists.

Stevens tried deploying a box-and-one defense on Booker a few times, a tactic he said he last tried when using a box-and-two on LeBron James and Kyrie Irving in the conference finals three years ago.

“It caught me off guard,” Booker said. “But then Mikal hit two big shots and they had to get out of it. So that was big-time.”

Despite the lulls and the deficits and the fact that the Celtics trailed for the final 46 minutes of the game, they did make one of their usual late runs to give the fans here on this snowy night hope, even if it was only fleeting.

In this case they trailed, 114-102, with less than two minutes left when Booker was called for a clear-path foul that gave the Celtics two free throws and possession. After Gordon Hayward hit the foul shots, Smart poured in his 10th 3-pointer.

Then two free throws and a dunk by Daniel Theis improbably made it 114-111 with a minute left. Bridges rolled in an 8-footer with 36.9 seconds remaining to give the Suns a bit more cushion. After a timeout, Smart lobbed an inbounds pass to Hayward for an alley-oop, but Hayward said he was caught between laying the ball in and dunking it, and he missed, essentially extinguishing the Celtics’ chances.


“Should have just went up and dunked it,” Hayward said.

Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him on Twitter @adamhimmelsbach.