The defeat dropped Los Angeles -- one of the oddsmakers' favorites to win the championship -- to 8-9 with more than a fifth of the season in the books.
"It's never, 'We got 65 games left,'" James said when asked if he can take the long view considering the Lakers' early injuries and how much of the 82-game regular-season slate remains. "We damn sure need to play better, no matter who is in the lineup. We have our system and we need to obviously fast-track it and get better with it so we can play, no matter who is out on the floor, we can play at a high level. ... There's no level of panic, but there should be some sense of urgency any time we take the floor."
James played for the first time in 2 weeks because of an abdomen strain and showed signs of his old self, registering 23 points on 10-for-16 shooting, six rebounds, two assists and two steals, but only three of his shot attempts came in the paint, which could be seen as a sign of the caution the 19-year veteran played with, dealing with his third significant injury in the past four seasons.
"Physically I felt OK and good enough to know that I can trust my body and get out and play tonight," James said. "So I'm more looking forward to seeing how I'm feeling tomorrow when I wake up. That is the telltale sign if I'm moving in the right direction with my injury."
Who knows what direction the Lakers are headed, however.
Boston outrebounded Los Angeles 51-33 despite starting center Robert Williams III (averaging a team-best 9.2 rebounds per game) out of the lineup.
"I mean ... rebound," said Russell Westbrook. "Ain't too much you can do about it. Just go get the ball ... simple as that."
The Lakers, who led by as many as 14 in the first half, saw their third-quarter woes continue, with the Celtics breaking things open with a 33-21 quarter out of the break.
"We have to get committed to playing as a team offensively," said Lakers coach Frank Vogel. "And when we do, like we saw in the first quarter, it looks beautiful and you see the potential of what we can be. But we got into holding the ball too much and not playing for each other enough. But that's part of learning each other and building that cohesiveness and the right habits. And then defensively, guys are going to have big roles if they commit to the defensive side. And if they don't, they're not. It's that simple."
The 130 points by Boston were the most the Lakers have allowed all season.
"We can go out and compete every night, but I don't think it's our offense. I think it's our defense, honestly," said Anthony Davis, who led the Lakers with 31 points. "We've just got to do a better job on the defensive end."
For Westbrook, who was outperformed by the point guard he was brought in to replace, Dennis Schroder -- as the Boston guard had 21 points, six assists and six rebounds to Westbrook's 12, six and four -- there was an element of déj vu. It was another frustrating night for him and his new team as they try to come together.
"I think the reality of it is everybody on the outside have really high expectations of our team, as they should," Westbrook said. "But the reality of it is we haven't really played with each other realistically, and nobody cares and everybody asks the same question, and I'm tired of giving the same answer to the same question every time we lose.
"It's like, 'Hey, how long do you think it's going to take?' We don't know. When we win, it's still going to take some time. So the reality of it is, throughout the season, there's going to be ups, there's going to be downs. It's now what you do as a team. You can pull apart, or you can come together and figure it out."
The Lakers are still without Kendrick Nunn (right knee) and Trevor Ariza (right ankle), who have both yet to appear in a game this season. And rookie swingman Austin Reaves continues to be sidelined with a hamstring strain.
James said he would like to see the team settle on a consistent look -- either going big, with DeAndre Jordan and Dwight Howard getting the lion's share of the minutes at center, or small, with Davis at the 5 -- and sticking to it.
He also doesn't want the team to run from its struggles.
"It's never as bad as it may seem, and it's never as good as it may feel," James said. "So I stay even-keeled throughout the whole journey. I understand this is a huge [undertaking]. It's a process for us. And I've always felt comfortable when things are uncomfortable, so I look forward to the process of us trying to get better.
"And us getting better. Not trying. We will get better. We will improve."
Jayson Tatum goes for 37 as Celtics use big 2nd half to beat Lakers
Jayson Tatum has another tremendous night, contributing 37 points on 13-of-26 shooting, as the Celtics top the Lakers 130-108.