And yet, the Celtics felt just fine. They couldn't have played much worse in the first half, committing 10 turnovers and giving up nine offensive rebounds to Miami -- which allowed the Heat to take 14 extra shots.
"We weren't playing our best, in a lot of ways," Celtics coach Ime Udoka said. "Sometimes, all it takes is one guy getting back to his average game."
No one was playing worse than Jaylen Brown. He went 2-for-7 from the field and committed four turnovers -- all in the first quarter.
Then the second half started. And as it played out, Brown wound up being the face of the team's turnaround.
Brown's 19-point, 0-turnover second half -- coupled with an 18-point second half from Jayson Tatum -- allowed Boston to finally break open what was a rock fight in the first half, as the Celtics went on to win 93-80 over the Heat, moving Boston to within one victory of its first trip to the NBA Finals in 12 years.
"Same player," Brown said from the first half to the second. "Just had to get settled in. That's it. As the game wears on, some of that energy, some of that intensity starts to wear off, so the game opens up a little bit. The game opened up for me in the second half.
"I didn't want to get down. I didn't want to look into the past, think that this game was over. My team needed me to come out and respond.
"First half was s---. Threw it away. [Just] come out, play basketball in the second half."
It was unclear whether Boston was going to be able to follow through on Brown's instructions after yet another ugly stretch of basketball in this series for the Celtics in the first half of Game 5. The difference from the other periods when Boston has gone off the rails in this series, however, is that the Celtics didn't allow the Heat to break the game open.
Instead, things were just as ugly on Miami's side of the ledger. While Tatum and Brown were combining to go 10-for-33 in the first half and the Celtics were throwing the ball around, Miami couldn't hit anything either. Its starting backcourt of Kyle Lowry and Max Strus combined to go 0-for-15 from the field and 0-for-12 from 3-point range for the game. Jimmy Butler, playing through a knee issue, finished 4-for-18. And overall, the Heat were a dismal 7-for-45 from 3-point range.
"You've got to enjoy this," Heat coach Erik Spoelstra said. "You do. You know, if you want to break through and punch a ticket to the Finals, you're going to have to do some ridiculously tough stuff. Getting on to Boston and figuring that out collectively, those are the emotions and the breakthroughs that you have that you remember the rest of your life. Bring this thing back on the 29th. That's all we talked about in there."
It was a game that, like the rest of this series, will never be called pretty. But for the Celtics -- a team that has built its remarkable midseason turnaround around a suffocating defense -- it was the latest example of the physicality they have prided themselves on throughout the playoffs.
"I think the mental stress and strain we put on some teams with our defense has worked and carried us through the playoffs at times," Udoka said. "You saw in the Brooklyn series, guys started to wear down. Game 7 [last round against the Milwaukee Bucks, Giannis] Antetokounmpo slowed down some. But having all those bodies to continue to throw at people wears down on them physically and mentally, making it tough, as long as we don't give them easy baskets in transition.
"With our guys, we're always confident they'll get it going and figure it out eventually."
Brown and Tatum certainly did so in the second half. After those early struggles, Brown went the final three quarters without a turnover. And in a game crying out for someone -- anyone -- to make a shot after that first-half brickfest on both sides, Brown stepped up to the plate in the second half.
He hit the final shot of the third quarter (a tough midrange bucket) and the first of the fourth (a triple on the wing) to push Boston's lead into double-digits for good. He made sure it stayed there by scoring 13 points in the fourth quarter on 5-for-6 shooting.
"Just guys getting settled in, kept being aggressive, stop turning the ball over," Brown said. "We gave them a lot more shots than we had in the first half. We was only down by five. We knew if we took care of it, we would get some open opportunities and knock 'em down.
"So just continue to play basketball, be aggressive. That's why basketball is 48 minutes."
It was a similar turnaround for Tatum, who was repeatedly grabbing at his shoulder throughout the first half, as he was clearly laboring from the nerve issue that briefly knocked him out of the fourth quarter of Game 3.
But Tatum kept trying to make plays for others in the first half and eventually finished the night with 22 points, 12 rebounds and 9 assists in over 44 minutes, as he -- like Brown -- eventually settled into a rhythm as the second half progressed.
"Yeah, it was bothering me," Tatum said. "We just figured it out.
"Obviously, they're a really good team. Both teams play hard, compete and things like that. But guys like [Derrick] White, obviously [Marcus] Smart being out there, just his presence, and JB made some big shots. Everybody contributed from the beginning 'til the end."
Now, the series heads back to TD Garden, where Boston -- in its sixth trip to the conference finals since last making the NBA Finals -- will have a chance to take that final step into the league's championship round.
But during a postseason that has seen so many twists and turns already for the Celtics -- including coming back from the exact same deficit the Heat find themselves in, down 3-2 on the road in Game 6, to beat the Bucks in the conference semifinals -- Boston knows its job is not done.
"The mindset and the talk that we had after the game was we was down 3-2 last time, had to go on the road and win a Game 6, and we did," Tatum said. "We can't think that it's over with. We need to go back home like we're down 3-2, with that sense of urgency that it's a must-win game, not relaxing because we're up.
"It's possible [for Miami to come back]. Obviously, we did it last series, so knowing that, talking about that, obviously enjoying this one, but not being satisfied knowing that we still got things to clean up, we still need to play better. The job's just not finished yet."