Find the decisive blow (difficulty 1575)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. f7–a2 key move
  2. f2–d3
  3. b6–c4

What makes it

A queen move and 3 points of material given up: mate in nine. The key move is neither check nor capture — a quiet shot the position cannot answer. 17 half-moves of forced play.