Saavedra’s 6.c8=R!! — Chess Library

The pawn reaches the eighth rank, but becoming a queen throws the win away. Promoting to a rook changes the geometry and creates two threats Black cannot meet together.

Lesson

White to move. Main line: 6. c8=R Ra4 7. Kb3

6.c8=Q? allows ...Rc4+!, skewering the king and new queen. The apparently weaker 6.c8=R!! removes that diagonal vulnerability.

The rook promotion threatens both mate on a8 and the enemy rook. After 6...Ra4, 7.Kb3 preserves the win.

Underpromotion is not decoration here. It is the only move that wins, which makes the Saavedra position one of chess composition’s clearest examples of geometry outweighing material value.