The Celtics’ return to TD Garden for Game 5 frames the most consequential test of Philadelphia’s postseason resolve. A 3-1 series deficit, according to NBA historical data, has produced a comeback in only 13 of 277 instances. For the Sixers, the margin for error has vanished. Game 5 presents not merely an elimination threat but a referendum on whether Joel Embiid’s hobbled knee and James Harden’s inconsistent rhythm can produce two consecutive victories. Boston, by contrast, has momentum and home-court advantage after stealing Game 4 on the road. The tactical adjustment from Coach Doc Rivers—specifically, how Philadelphia defends Jayson Tatum’s pick-and-roll without overcommitting—will determine whether the series returns to Philadelphia or ends Wednesday night. The unresolved tension: the Sixers have not won a Game 5 on the road under Rivers.