Celtics just stumbled into test they haven't faced in over a decade

A 0-3 start to the Boston Celtics season hasn't caused panic, but it should certainly cause reflection.

Jaylen Brown, Payton Pritchard, Joe Mazzulla, and Derrick White | Jonathan Daniel/GettyImages | Maddie Meyer/GettyImages | Nic Antaya/GettyImagesDETROIT — As Joe Mazzulla paced the sidelined at Little Caesars Arena on Sunday afternoon, frustration seeped through to the surface. Almost every time he got up, he either say back down in a heap or threw his hands up in exasperation.

Most of the time, it was a Detroit Pistons offensive rebound that did it. They finished with 19. Other times, an untimely Boston Celtics foul was at the root of the issue. A 17-point first-quarter lead slowly…