Find the decisive blow (difficulty 1595)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. b4–a3 key move
  2. d5–e3
  3. f2–e3
  4. h6–e3
  5. g1–g2
  6. e3–h6
  7. a3–a7
  8. f8–e8

What makes it

A 3-point investment, and the attack wins by force. No check, no capture: just a quiet move, and the defence caves in. 8 half-moves of forced play.