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Base: Queen first, lose (or draw) later

What is the most economical pawn endgame position where Black queens first but White wins, White pawns no higher than 4th rank on time of Black queening?

(FYI, Ke6 + 8 pawns on the 5th seem to win against Qd1+Ke1, but Ke5 + 8 on the 4th lose, trusting Stockfish)

(added so Noam can move his answer here, where it fits better. And I can post my rank 2 solution)

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2 Answers 2

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4th rank, 4+1 pawns:

[Title "White plays and wins"]
[FEN "8/8/8/8/kPP5/2P5/1P5p/K7 w - - 0 0"]

1. Ka2 h1=Q 2. b3#

(Also works with 3+2 pawns, removing wPb4 or wPc4 and adding bPa5 or bPb5 respectively. All of these are drawn with bPh2 moved to c2, when Black answers 1 Ka2 with c1=N+!)

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  • [copied from my answer to chess.stackexchange.com/questions/40655 as requested]
    – Noam D. Elkies
    Commented Sep 26, 2022 at 2:32
  • THX for moving! BTW, since I defined "less white pawns" for record judging purposes, your alternatives "score" better.
    – Hauke Reddmann
    Commented Sep 26, 2022 at 9:03
  • In the 4+1 version with bPc2, I am not sure Black can save the game after 1.Ka2 c1N+! 2.Kb1 and 3.Kc2...
    – Evargalo
    Commented Sep 27, 2022 at 7:12
  • I wasn't sure either but Syzygy says it's a draw, noting the resource 1 Ka2 c1N+! 2 Kb1 Nd3! 3 Kc2 Nxb2! (other moves lose).
    – Noam D. Elkies
    Commented Sep 27, 2022 at 13:51
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Not a record but even all-on-base-rank pawns can mate:

[FEN "8/8/8/4ppp1/1K2kpp1/8/p2PPP2/8 w - - 0 1"]

1.Kc4! and queening is immediate mate, f3 only delays a move.

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  • 1
    We immediately save two bP's by shifting the diagram two squares to the right. (Then 1 Ke4(Ke5) threatens two different mates, but you asked only for a forced win, not a sound problem.)
    – Noam D. Elkies
    Commented Sep 25, 2022 at 21:46
  • @NoamD.Elkies: Yup. Shame on me I saw it only five seconds after posting :-)
    – Hauke Reddmann
    Commented Sep 26, 2022 at 20:45

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