Find the decisive blow (difficulty 1680)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. d6–d7 key move
  2. b3–d1
  3. c1–d1

What makes it

A pawn move and a 5-point sacrifice: mate in ten. No check, no capture: just a quiet move, and the defence caves in. It calculates 19 plies deep.