By Michael Hurley, CBS Boston

BOSTON (CBS) — The Patriots got off to a perfect start Sunday night in the AFC Championship Game. But then things changed significantly on just one snap.

That snap came at the 1-yard line, on a third-and-goal early in the second quarter. The run game had been working with great success to that point, but Josh McDaniels decided to dial up a playaction pass to try to catch the Chiefs defense off guard.

It didn’t work, as four defenders dropped into coverage and just one player — Rob Gronkowski — ran out for a route.

Tom Brady uncharacteristically threw the ball into traffic. Linebacker Reggie Ragland made the easy interception, immediately killing the Patriots’ chances of taking a two-possession lead.

The Patriots led 7-0 at the time of the pick.

Brady had made 78 consecutive red zone passes in the playoffs without throwing a pick. He had also thrown 237 passes in the playoffs without throwing an interception.