The Boston Celtics were on the road without their best player against a team that was undefeated in the playoffs and had blown them out the last time they were on the same court. So their last-second win over the Cleveland Cavaliers on Sunday night was more than surprising. It was the single biggest statistical upset of the entire NBA season.

That kind of shocker is not supposed to happen in the conference finals simply because the point spread between two of the best teams in the league should never be wide enough to let...