If an Opportunity Attack occurs before the trigger, how does a Quarterstaff work with Polearm Master?

@Dastion If an AoO occurs just before the trigger, how does a Qtrstaff work with Polearm Master? Aren’t they out of reach? The Polearm Master feat is an exception to the opportunity attack rule: “… when they enter your reach.”

— Jeremy Crawford (@JeremyECrawford) August 22, 2014

@Dastion For Polearm Master to work, the provoking creature has to be within your reach, not right outside it.

— Jeremy Crawford (@JeremyECrawford) August 22, 2014