8/8/8/5kp1/p7/P4K2/1P6/8 b - - 0 1

White just played Kf3, thereby gaining the opposition.

If there were no queenside pawns, what is on the kingside would be a "book" draw. That's because the White king can maneuver himself into a stalemate position on his first rank.

But in this position, if the White king can't move, White has to move the b pawn to b3, or to b4 via b3. In either event, Black's a pawn takes it, queens, and wins for Black.

Or does it?

  • When I follow your link, it is in a "new game" state - could you update it with your FEN? – Ghotir Mar 23 '16 at 19:39
  • @Ghotir: Apparently, I don't know how to do this. I added a note with the position. There are only two kings and four pawns. – Tom Au Mar 23 '16 at 19:43
  • Not a problem. Description worked. One of the longer-time users will probably set up a board in your question for you. In the meantime, to make it easier for others: 8/8/8/5kp1/p7/P4K2/1P6/8 b - - 0 1 – Ghotir Mar 23 '16 at 19:45
  • 1
    This is a position with 6 pieces on the board. These are called 6 men tablebase and their result can be checked online here. The position is lost for White... – AlwaysLearningNewStuff Mar 24 '16 at 1:05

Black wins.

Black has a distant passed pawn and Blacks pawns are more advanced. White is bound to defend against g-pawn, while Black can do anything with a and b pawns. And White cannot win a pawn race, because Black is more advanced.

[Event "Original Position"]
[Site ""]
[Date ""]
[Round ""]
[White ""]
[Black ""]
[Result "0-1"]
[FEN "8/8/8/5kp1/p7/P4K2/1P6/8 b - - 1 2"]
[Setup "1"]

2... g4+ 3. Kg3 { Option 1, defending against g-pawn, fails.}  ( 3. Ke3 { Option
2, counter attack on the other side, which fails also, because Blacks pawns are
more advanced, Black wins the race.}  3... Ke5 4. Kd3 Kf4 5. b4 axb3 6. a4 g3
7. a5 g2 8. a6 g1=Q ) 3... Kg5 4. Kg2 Kf4 5. Kf2 g3+ 6. Kg1 Kf3 7. Kf1 g2+ 8.
Kg1 Kg3 9. b4 axb3  

However, if Black wouldn't have a-pawn that advanced, White could catch Black and avoid promotion after dealing with g-pawn.

For example:

[Event "Queenside Pawns Shifted"]
[Site ""]
[Date ""]
[Round ""]
[White ""]
[Black ""]
[Result "1/2-1/2"]
[FEN "8/8/8/p4kp1/P7/1P3K2/8/8 b - - 1 3"]
[Setup "1"]

3... g4+ 4. Kg3 Kg5 ( 4... Ke5 5. Kxg4 Kd5 6. Kf4 Kc5 7. Ke5 ( 7. b4+ axb4 8.
Ke3 b3 9. Kd2 Kb4 10. Kc1 Kc4 11. Kb2 Kb4 12. a5 Kxa5 13. Kxb3 ) 7... Kb4 8.
Kd4 Kxb3 9. Kd3 Kxa4 10. Kc4 { Black king is trapped. Draw.}  ) 5. b4 ( 5. Kg2
$2 $19 Kf4 6. b4 axb4 7. a5 b3 8. a6 b2 9. a7 b1=Q 10. a8=Q Qc2+ 11. Kg1 Qd1+
12. Kg2 Qe2+ 13. Kg1 Qe1+ 14. Kg2 Qg3+ 15. Kf1 Qf3+ { And black takes
opposition, which is necessary to promote g-pawn.}  16. Qxf3+ Kxf3 17. Kg1 Kg3
18. Kh1 Kf2 19. Kh2 g3+ 20. Kh1 g2+ 21. Kh2 g1=Q+ ) 5... axb4 6. a5 b3 7. a6 b2
8. a7 b1=Q 9. a8=Q { This is a bit complicated, but according to tablebase,
this is draw.}   
  • 1
    In a second position 3. ... g4+?? is a blunder. White King must move to g file anyway, so Black just loses a tempo. 3. ... Ke5! wins easily. – user58697 Mar 24 '16 at 21:27

The position is definitely lost for white.

You can convince yourself about this by checking in an endgame tablebase. White either has to allow the g-pawn promotion or let his king be "stalemated", forcing him to push the b-pawn and be checkmated soon thereafter.

[Title "Best play according to an endgame tablebase"] 
[fen "8/8/8/5kp1/p7/P4K2/1P6/8 b - - 0 1"]

1... g4+ 2. Kg3 Kg5 3. Kf2 Kf4 4. Ke1 g3 5. Ke2 Ke4 6. Kf1 Kf3 7. Ke1 g2 8. Kd2 g1=Q 9. Kc3 Qc5+ 10. Kd3 Qd5+ 11. Kc2 Ke4 12. b3 Qxb3+ 13. Kc1 Qa2 14. Kd1 Kd3 15. Ke1 Qe2# 0-1


[Title "Example scenario without g-pawn promotion"]
[fen "8/8/8/5kp1/p7/P4K2/1P6/8 b - - 0 1"]

1... g4+ 2. Kg3 Kg5 3. Kg2 Kf4 4. Kf2 g3+ 5. Kg2 Kg4 6. Kg1 Kf3 7. Kf1 g2+ 8. Kg1 Kg3 9. b3 {or b4; forced, since the king cannot move} axb3 10. a4 b2 11. a5 b1=Q# 0-1
  • That's what I thought, but I wanted to make sure. It's ironic that White loses even though he has two pawns to one on the queen side, whereas he draws with no queenside pawns. – Tom Au Mar 23 '16 at 20:18
  • @TomAu White has two pawns in queenside against one, but in a very bad formation. White cannot move without sacrificing a pawn. Plus, Blacks pawn is more advanced. Also, Black has a distant passed pawn, which creates often a winning advantage. – ferit Mar 23 '16 at 20:35
  • Don't copy tablebase lines as demonstration. Because tablebases select best moves according to distance to mate. Because of this, in your first pgn, White is doing senseless moves back and forth. Instead, you should demonstrate Whites defensive ideas. – ferit Mar 23 '16 at 21:01
  • @Saibot The second diagram clearly demonstrates whites intuitive defensive idea (blocking the g-pawn), while tablebase line shows the longest possible defense ("senseless" moves or not, this is how white can survive the longest, plus tablebase provides an absolute evaluation of the position). I assume you also are the one who downvoted, which as the answer is perfectly correct seems excessive, but whatever. – GloriaVictis Mar 24 '16 at 8:14

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