Under promotion of a pinned pawn to bishop

[lkaufman]

Hello together,
chess puzzle lovers will love this: A position from a real game where an under-promotion to bishop happens. And even better, a pinned pawn under-promoted.
If you ask me, this is a 1 in a million situation:

[d]4b3/1k1P4/1P6/1K3p2/5N2/8/8/8 w - - 1 67 bm dxe8=b

(Mate in 7 with underpromotion to bishop)
And here the complete game between Fruit 2.1 and OliThink 5.7.0:


[pgn]
[Event "?"]
[Site "?"]
[Date "2020.09.03"]
[Round "4256"]
[White "Fruit 2.1"]
[Black "OliThink 5.7.0"]
[Result "1-0"]

1. c3 e5 2. c4 Nc6 3. Qc2 Nf6 4. Nf3 e4 5. Ng5 d5 6. cxd5 Qxd5 7. h4 Nb4 8. Qd1
Qf5 9. d3 Bc5 10. Be3 exd3 11. exd3 Bxe3 12. fxe3 Ng4 13. Qd2 Qc5 14. Nc3 Qxe3+
15. Qxe3+ Nxe3 16. Kd2 f6 17. Nf3 Nxf1+ 18. Rhxf1 O-O 19. a3 Nc6 20. Nb5 Bf5
21. Nfd4 Nxd4 22. Nxd4 Bg4 23. Rae1 Rfe8 24. Nb5 Rxe1 25. Rxe1 c6 26. Nd6 b6
27. Rc1 c5 28. b4 cxb4 29. axb4 Rd8 30. Ne4 Be6 31. Rc7 Bd5 32. Ng3 g6 33. Ne2
Bxg2 34. Rxa7 Be4 35. d4 f5 36. Rc7 Bg2 37. Kc3 b5 38. Nf4 Bf3 39. Ne6 Re8
40. Ng5 Bd5 41. Nxh7 Re3+ 42. Kd2 Re6 43. Ng5 Rd6 44. Ke3 Rd8 45. Rc5 Kg7
46. Rxb5 Kh6 47. Nh3 Bc4 48. Rc5 Re8+ 49. Kf2 Re2+ 50. Kf3 Rc2 51. Nf4 g5
52. hxg5+ Kxg5 53. Nh3+ Kf6 54. Kf4 Bd3 55. Ke3 Bc4 56. Nf4 Bb3 57. Rxc2 Bxc2
58. b5 Ke7 59. d5 Kd6 60. b6 Bb3 61. Kd4 Ba2 62. Kc3 Kd7 63. Kb4 Kc8 64. Kb5 Kb7
65. d6 Bf7 66. d7 Be8 67. dxe8=B 1-0
[/pgn]

For information: OliThink 5.7.0 has a little bug, where it can't do underpromtions of pinned pawns. Promotion of pinned-pawns are already very rare, now who would ever think there was an underpromotion of a pinned pawn. An not artificially constructed, it's real.

It could only be detected because of that little bug in OliThink 5.7.0, after Fruit's move, it stalled. In OliThink 5.7.1 this bug is fixed.

I've never seen or heard of a competitive human master game in which underpromotion to a bishop was the only winning move, has anyone else here? However, while testing dedicated chess computers for ICD thirty years ago, I had one game that halted after a bishop underpromotion. When I checked it out, it was indeed the only winning move, and the other side wasn't programmed to recognize bishop underpromotion!
However, your example is much less special since underpromotion to a knight (which is often the only winning move) also wins. I suppose it is quite rare that bishop and knight work but rook and queen don't, but probably much more common than positions where only a bishop works.

[OliverBr]

However, your example is much less special since underpromotion to a knight (which is often the only winning move) also wins. I suppose it is quite rare that bishop and knight work but rook and queen don't, but probably much more common than positions where only a bishop works.

Still, underpromotion to a knight doesn't mate in 7, only to a bishop does.

Furthermore this puzzle here is very special, because the to-be-promoted pawn is pinned. Before this game was played I constructed artificially a situation in order to test this little bug:

[d]3b4/4P3/8/6K1/8/8/k1p1R3/8 w - - 0 1

There are 2 pinned pawns short of promotion. As everyone can see, pinned pawns cannot promote without capturing.

PS: Interestingly this position looks quite similar to the position we talk about, that was eventually played between Fruit2.1 and OliThink 5.7.0:

[d]4b3/1k1P4/1P6/1K3p2/5N2/8/8/8 w - - 1 67

[Dann Corbit]

I've never seen or heard of a competitive human master game in which underpromotion to a bishop was the only winning move, has anyone else here?

Tim Krabbe, of course, was the place to go:
https://timkr.home.xs4all.nl/chess2/minor.htm

Meanwhile, here are two cheeky underpromotion to bishop games:

Humiliation:
[pgn][Event "TBI-S-2007-P-0007"]
[Site "InterAjedrez/CXEB"]
[Date "2007.12.06"]
[Round "1"]
[White "Mendonca, Juliano Simao"]
[Black "Nunes, Jose Benigno"]
[Result "1-0"]
[ECO "C65b"]
[EventDate "2007.??.??"]
[PlyCount "153"]
[Source "Opening Master"]
[SourceDate "2018.05.29"]
[WhiteTeamCountry "USA"]
[BlackTeamCountry "BIH"]

1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4.Qe2 d6 5.c4 Bg4 6.O-O Nd7 7.Qe3 Nb4 8.Qb3 Bxf3 9.gxf3 Nc6 10.Bxc6 bxc6 11.f4 Nc5 12.Qf3 Qf6 13.d3 Ne6 14.f5 Be7 15.Be3 c5 16.Nc3 Ng5 17.Qg3 h6 18.Nd5 Nf3+ 19.Qxf3 Qh4 20.Nxc7+ Kd7 21.Nxa8 Rxa8 22.Qg3 Qf6 23.Bd2 Rb8 24.Bc3 Ke8 25.f4 Qh4 26.Qxh4 Bxh4 27.fxe5 Bg5 28.exd6 Rb6 29.e5 Be3+ 30.Kg2 Kd7 31.Kf3 Bg5 32.Ke4 Rb8 33.Kd5 Re8 34.e6+ fxe6+ 35.fxe6+ Rxe6 36.Rf7+ Be7 37.Rxe7+ Rxe7 38.dxe7 Kxe7 39.Bxg7 Kf7 40.Bxh6 Ke7 41.Kxc5 Ke6 42.d4 Kd7 43.d5 a6 44.b4 a5 45.b5 Kc8 46.b6 a4 47.Kc6 a3 48.d6 Kd8 49.d7 Ke7 50.b7 Kf7 51.d8=B Kg6 52.Bhg5 Kf5 53.b8=B Ke6 54.h4 Kf5 55.h5 Ke4 56.Rd1 Kf5 57.Kd5 Kg4 58.h6 Kf5 59.h7 Kg4 60.h8=B Kf3 61.c5 Ke2 62.Rd2+ Kf3 63.c6 Kg4 64.c7 Kf3 65.Rd3+ Ke2 66.Rxa3 Kf2 67.c8=B Kf1 68.Re3 Kg1 69.Re2 Kh1 70.Bh3 Kg1 71.a4 Kh1 72.a5 Kg1 73.a6 Kh1 74.a7 Kg1 75.a8=B Kh1 76.Kd4+ Kg1 77.Bh2# 1-0
[/pgn]

Style points:
[pgn][Event "CCRL 40/4"]
[Site "CCRL"]
[Date "2007.11.22"]
[Round "26.165"]
[White "Arasan 10.0 64-bit"]
[Black "Snitch 1.6.2 32-bit"]
[Result "1-0"]
[ECO "E32t"]
[Opening "Nimzo-Indian: Classical, 4...O-O 5.a3, 6...b6 7.Bg5 Bb7 8.e3 d6"]
[Annotator ""]
[Source ""]
[Remark ""]

1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Qc2 O-O 5.a3 Bxc3+ 6.Qxc3 b6 7.Bg5 Bb7 8.e3 d6 9.Nf3 Bxf3 10.gxf3 Nbd7 11.Be2 h6 12.Bh4 e5 13.dxe5 dxe5 14.O-O-O Qe8 15.f4 Ne4 16.Qc2 exf4 17.Rxd7 Qxd7 18.Qxe4 fxe3 19.Qxe3 Rfe8 20.Qd3 Qe6 21.Bf3 Qh3 22.Bg3 Rad8 23.Qc2 Rd4 24.Rd1 Qd7 25.c5 Re7 26.c6 Rxd1+ 27.Qxd1 Qe8 28.Qd5 a5 29.b3 Re1+ 30.Kd2 Re7 31.Kc2 Kh8 32.h4 f6 33.h5 Qa8 34.Be4 a4 35.b4 Qe8 36.Bd3 Qc8 37.Kc3 Qb8 38.Bc2 Qa8 39.Bf4 Qg8 40.Qxg8+ Kxg8 41.Bf5 Kf8 42.Bd7 Re5 43.Kd4 Rxh5 44.Bxc7 Ke7 45.Bxb6 Rh4+ 46.Kd3 Rh5 47.Bg4 Rd5+ 48.Kc3 h5 49.c7 hxg4 50.c8=Q Rg5 51.Qg8 Kd6 52.Kd4 Ke7 53.Bc5+ Rxc5 54.bxc5 f5 55.Qxg7+ Ke6 56.c6 g3 57.Qf8 gxf2 58.c7 f4 59.c8=B# 1-0
[/pgn]