Lesson
White to move. Main line: 1. c7 Rd6+ 2. Kb5 Rd5+ 3. Kb4 Rd4+ 4. Kb3 Rd3+ 5. Kc2 Rd4 6. c8=R! Ra4 7. Kb3
White is a pawn against a rook, so the pawn must queen — and the rook keeps checking to stop it. Each check drives the king one square along, and the tablebase says only 1. c7 keeps the win; every other move here is a draw.
At move six, 6.c8=Q? allows ...Rc4+! and ...Rxc8, while 6.c8=R! avoids the skewer and threatens mate. After ...Ra4, 7.Kb3 preserves both threats. Underpromotion is not a flourish here; it is the only win.
The line shown is tablebase-perfect — every move is the objectively best one, for both sides.
A position with one move
White has a pawn on the sixth and a king in front of it; Black has a rook. Every natural king move draws. Only 1.c7 wins, and the engine is unambiguous about it — the four alternative king moves all evaluate as dead level.
That gap is what makes the position a study rather than an exercise. There is no general principle that picks 1.c7; you have to see the whole sequence.
The rook checks, the king walks
Black checks from the side and White’s king walks down the board towards the checks — b5, b4, b3, c2. Each step reduces the number of squares the rook can check from, and the king is heading for shelter next to the pawn.
Nothing here is clever yet. It is a technique: when a rook checks a king that is escorting a pawn, walk towards the rook, not away from it.
The underpromotion
The point arrives at the end. Promoting to a queen allows Black to force stalemate, so White promotes to a rook instead, threatening mate and forcing Black to give up the rook.
This is where the position gets its name: Fernando Saavedra spotted the rook promotion in a study that had been published as a draw. The correction is more famous than the original.
1.c7: The only winning move — evaluated around +2.3 and the sole line that reaches the promotion.
1.Ka7, 1.Ka6, 1.Kb7, 1.Kc7: All exactly 0.00. Black’s rook gets behind the pawn and the position is a straightforward draw.
When a rook checks the king escorting your pawn, walk the king towards the checks to cut off the checking squares.
Stalemate is a resource for the defender — check for it before you promote automatically to a queen.
Underpromotion is almost always about avoiding stalemate or delivering an immediate threat a queen cannot.
Source: The Saavedra position — https://en.wikipedia.org/wiki/Saavedra_position