Namely, it knows it needs to finish things now.
There was no time for smiling, laughing or joking around when the C's met up in Waltham. This was a team singularly focused on Kevin Garnett's decree after Tuesday's Game 2: They can't go back to Cleveland. They can't let this series come down to a deciding Game 7.
In other words, Game 6 is their Game 7.
"That's the way we've got to look at it," Glen Davis said on Wednesday. "Game 7, last game. We've got to finish it. We've got to close it out.
"It's the biggest game of the series. It's a close-out game. People don't realize how much we have on our backs. They think, 'Oh, we're going home with the lead,' but if we lose this game at home, we've got to go back to Cleveland. We know we can win there, but at the same time, that's their house. That's their environment. They play there more than we do. It's a tough situation."
This is the Celtics' first time since acquiring Garnett that they've been without home court. This is the first time they've gone in knowing, if their series goes seven, that that Game 7 wouldn't be in their own building.
The Celtics know the importance of finishing the job at the TD Garden. Because back in Cleveland against a hungry LeBron James, anything can happen.
"Listen, guys," said Celtics coach Doc Rivers. "We have one home game left in this series. We haven't done anything. And I've made that clear. And you know you're going to get Cleveland's best shot. You know LeBron's going to play an amazing game. And we're going to have to absorb that and still win the game."
The C's take on the Cavs at 8 p.m. on Thursday.