Winning blow: pawn to b8 (b7·6)
c9-16673naming tag (square·N)Opens in the app if installed, otherwise downloads the APK.
The tactical motive
Chess960 twist: use the unusual starting setup of the pieces.
A fork made possible by the Chess960 piece placement.
Winning tactic: there is a move that gains a decisive advantage — find it.
Difficulty 1200 ShuffleRating — club-player level.
White to move — find the best continuation
How to recognize this tactic
In Chess960 the pieces start on unfamiliar squares, so tactics appear earlier and from unusual angles. Do not trust classical patterns — read the actual lines of the bishops, the rooks and the queen from where they really stand in this position.
A set-up fork needs one preparing move before the fork lands — a check that drives the king onto the forking square, or a capture that lines the targets up. Find the preparation first, then the fork it makes possible.
This position hides a concrete tactic that wins material or mates. Start with the most forcing candidate moves — checks, captures and threats — and calculate each to a clear end before choosing; the winning line is usually the one the opponent cannot meet.
General method: before you move, list the forcing candidates — every check, every capture, every direct threat — and calculate those first. The solution to a tactic is almost always among them.
Position on the board
White: king c2, rook e1 b3, bishop a1, knight h1, pawn d2 f2 h2 b7.
Black: king a7, queen d5, rook e6, bishop f8, knight f4 g5, pawn e5 c7 g7 h7.
9 white and 10 black pieces are on the board; the puzzle position arises after move 20.
The position in numbers
Black are ahead by 7 points of material (20 against 27; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on c2, the black king on a7.
It is White to move on move 20, with 40 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 4 pawns, Black 4. Files fully open (no pawns of either colour): a — natural highways for the rooks and queen. Half-open for White: c, e, g.
The White king has 5 empty squares to step to right now — the fewer they are, the closer a mating net.
Solution & explanation
Main line
20. b8=Q+ Ka6 21. Qc8+ Ka5 22. Bc3+ Bb4 23. Qxc7+
Why it works
- Great move! pawn to b8 keeps the pressure (#6).
- Well found: queen to c8 (#5).
- Precise: bishop to c3 is the top choice (#4).
- Best move. queen to c7 is exactly what the engine plays (#3).
- You win a piece — the pawn.
- If instead Ka6, then Qc8+ and you win the pawn.
Move by move
- 20. b8=Q+ — pawn to b8 with check
- Ka6 — king to a6
- 21. Qc8+ — queen to c8 with check
- Ka5 — king to a5
- 22. Bc3+ — bishop to c3 with check
- Bb4 — bishop to b4
- 23. Qxc7+ — queen to c7 (capture) with check
Types in this puzzle
Setup fork
The random setup allows a fork that classical chess never sees.
A setup fork is a double attack that exists only because of the unusual starting squares — in classical chess these targets never stand side by side. Look for pairs of undefended pieces on your opponent's back rank and for squares from which a knight or pawn hits both at once. Such forks usually appear within the first moves, before the pieces disperse. In every new position, note right away which starting pieces are defended by no one.
Only move
Everything else loses — find the only move that holds.
An only move is a position where everything loses except one single continuation. You cannot play "by hand" here: run through fundamentally different defenses — run away, block, trade, counterattack — and discard the ones that fail. The hallmark of these puzzles is that the obvious moves lose quickly while the solution often looks strange. First understand exactly what the threat is — then the one saving move reveals itself.
Promotion
The pawn reaches the last rank and becomes a queen — decisively.
Promotion turns a pawn on the last rank into a queen and rewrites the evaluation on the spot. In tactics the passer rarely walks in for free — usually a sacrifice clears its path. Count the tempi: how many moves does the pawn need, and can the defender stop it in time? And watch the promotion square itself — it must be out of enemy reach or won by force in your combination.
About this position
These pieces come from starting position #898.
SP-898 · BastionScout — A knight on the a- or h-file, king on c or f — the mirror twin lands here as well.
The king starts on c1, the rooks on b1 and e1, the queen on d1.
The king already stands on c1, so castling long moves only the rook, from b1 to d1.
A bishop starts in the corner on a1: it has a single diagonal, which the b-pawn unlocks, running out to h8.
The second rank carries 2 pawns with no defender at all: a2, h2.
The setup belongs to the BastionScout family; read right to left it becomes position 55.
The engine's main line opens with f4.
Morozov Balance Index: 51 of 100 — class C — noticeable edge. Engine evaluation of the starting position: +26 centipawns for White (depth 45, 400 000 000 nodes).
Explore position #898Provenance
Mined from the project's engine self-play games.
Pack 008 · SP-898
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