Yes. If the C's started the game like they did in that small 3rd quarter showing of effort, the hole wouldn't have been so great from the get-go. Whether it's sustainable, I don't know, but they can't afford to have such terrible starts in this series.
I do think the starters (especially IT, short on shots and a couple FT's) were tired. Mentally, they need to be prepared to grind it out. Like KG, Perk, and PP said on Area 21, this Celtics team has grit. Too bad it wasn't on full display tonight, but I expect it to be back for game 2!
EDIT: More Jaylen please! He showed a lot of hustle with his rebounding, and poise for a rookie on a big stage. Didn't get intimidated like most of the team..