"I played like shit, bottom line," Adebayo told reporters after Game 5 of the Eastern Conference finals. "I can't - I put that game on me. It's not my teammates' fault, it's not my coaches' fault. Just me."
The 23-year-old reasoned that he "missed too many shots" he should have made.
Entering the contest averaging 21.5 points per game on 60.4% shooting, Adebayo shot just 5-of-11 (45.5%) from the floor Friday; even with 3-of-4 shooting from the free-throw line, his final tally of 13 points marked his lowest scoring output so far this season.
Adebayo, who was named to the NBA's All-Defensive second team earlier in September, added that his impact on the defensive end wasn't up to his usual standard.
"I wasn't giving the defensive effort that I should have been," he said. "I don't think I was communicating fast enough. I feel like I was a step behind today."
Perhaps seizing on Adebayo's inconsistencies, Celtics wings Jayson Tatum and Jaylen Brown combined for 59 points - albeit on relatively modest 20-of-45 (44.4%) shooting. Boston center Daniel Theis, who had averaged 6.5 points per game in the series ahead of Game 5, dropped 15 points.
With the sting of Friday's loss fresh in his mind, Adebayo said he planned to get into the gym and go over game film ahead of Sunday's Game 6.
"I just can't do whatever I did this game," he added. "That's got to go. That's behind me now. Now's looking forward. My mentality has to be, 'I have to be better for my teammates.'"