Celtics coach Doc Rivers said his team lost its composure in the second half of Game 4 on Friday night against the 76ers.
"And once we did, we never really returned to playing basketball the way we played in the first half," he said.
Rivers took responsibility for not being able to get his team back on track.
"You know, whenever that happens I always think that's me," Rivers said. "I always think there's something the coach can do to slow them down, to get them back in their sets, to get them back in their rhythm, and I couldn't do it."