Find the decisive blow (difficulty 1545)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. a1–h8 key move
  2. h4–g5
  3. f7–f6
  4. g1–h3
  5. b7–b6
  6. f2–f4
  7. e7–e5
  8. f4–f5

What makes it

1 points of material given up tears the position open and wins. A quiet move, soft as anything, and yet there is no reply. 8 half-moves of forced play.