Goal or offside play?

[Robert Goodman]

A1 is taking a corner kick, and goalie D1 is closely marking A2 in the middle of the penalty area. The kick is a head-high hard one that seems aimed at A2. However, A3 comes running from afar into the PA on the side closer to A1, and heads the ball into the near part of the goal. At the time A3 headed the ball, he was farther from D's goal line than was A2, and no player of D besides D1 was closer to D's goal. D1 had no chance at the ball where he was positioned, and as long as he thought the corner kick was going to A1, he was going to stay there. A2 was nowhere near D1's line of sight to A3 or the ball.

Do you disallow the goal for A2's being offside and clearly having had the attention of D1 when A3 played the ball? Or do you allow the goal because at the instant A3 played it, A2's offside position was irrelevant in getting D1's attention?