Embiid scored 12 points on 5-of-5 shooting in the first quarter after getting a number of early opportunities in the post. But the Celtics brought double-teams to force turnovers and Embiid ended up with just 15 shots for the game, finishing with 26 points and 16 rebounds.
"Obviously not enough [shots]," Embiid said. "I've got to be more aggressive. Maybe we need to call some more plays but I don't know. That's another thing we've got to fix going into Game 2."
The Celtics, who are at a size disadvantage and often struggle with bruising centers, had a game plan ready. They pressured the ball on the perimeter to make it harder to get passes in to Embiid, and then when he got it inside, Boston would routinely bring the doubles from his blind side.
That led to seven Philadelphia turnovers -- three of them by Embiid -- in the first quarter, undercutting the strong start. Those issues led coach Brett Brown to go away from calling as many post-up plays for Embiid the rest of the way.
Embiid finished with five turnovers for the game and the 76ers had 18 as a team, leading to 21 Celtics points that played a major role in the outcome.
"This is the double-edged sword where you have to figure out what line do you want to walk," Brown said. "This overplaying the volume of just smashmouth, bully-ball post-ups; if you do it all the time it comes with some level of punishment if you're not careful."
This has been a routine back-and-forth with the 76ers for months. When the team arrived for the restart, Embiid announced that he planned to be more assertive in demanding touches. Meanwhile in practices leading up to the seeding games, Brown ran a daily boot camp of putting Embiid through drills to handle double-teams to prepare him for this challenge.
With All-Star Ben Simmons out for the season with knee surgery, there are hopes Embiid can carry the 76ers with huge performances against the Celtics. But while the numbers looked OK Monday, both aspects of the game plan were left wanting.
"I've got to do more. I got one job to do, to carry us," Embiid said. "I'm going to need my teammates to help but I need to do more. I've got to take more shots, I've got to be more aggressive, I've got to help my teammates."
The Celtics suffered a setback when forward Gordon Hayward left the game late in the fourth quarter with a sprained right ankle. He was already experiencing swelling and was headed for an MRI late Monday. If the injury causes Hayward to miss time, the already thin Celtics could be more vulnerable.
Brown was taking an optimistic view despite falling behind in the series.
"You can't minimize the fact the losing stinks," Brown said. "But I feel like there are answers to the questions of why."