Answers.Body: <p>Of course this has happened, but it depends on your definitions. With the definition that &quot;a blunder is a move that changes the game-theoretic state of the game&quot; (e.g. &quot;draw&quot; to &quot;loss&quot; or &quot;win&quot; to &quot;draw&quot;), then here's an <a href="https://chessbase.in/news/Grischuk-versus-Ding-Liren-World-Cup-2019" rel="nofollow noreferrer">example</a> where both Ding Liren and Alexander Grischuk were blissfully unaware of the blunder until after the end of the game.</p>
  <pre><code>[FEN &quot;&quot;]
  [White &quot;Grischuk, Alexander&quot;]
  [WhiteElo &quot;2759&quot;]
  [Black &quot;Ding, Liren&quot;]
  [BlackElo &quot;2811&quot;]
  [Result &quot;1/2-1/2&quot;]
  [startply &quot;26&quot;]
  
  1. d4 Nf6 
  2. c4 e6 
  3. Nf3 d5 
  4. g3 dxc4 
  5. Bg2 a6 
  6. O-O Nc6 
  7. e3 Rb8 
  8. Nfd2 e5 
  9. Bxc6+ bxc6 
  10. dxe5 Ng4 
  11. Nxc4 Be6 
  12. Qe2 h5 
  13. Rd1 Qc8 
  14. Qf3? Bd5 
  15. Rxd5 cxd5 
  16. Qxd5 Qf5! {Black threatens ...Qxf2+ and mate.} 
  17. f3! {Both Grischuk and Ding Liren saw this far and could not see a refutation of this move.} Qc2! {Black threatens ...Qxc1+, and ...Qf2+ followed by mate.} 
  18. Qc6+! {18.Nbd2? Qd1+ 19. Kg2 Qe2+ wins. White has to move the Queen so that the d2-knight is no longer pinned, and Nf1 becomes possible.} Kd8 
  19. Nbd2 Qd1+ 
  20. Nf1 {If White gets a single free move here, 21. Bd2 intending 22. Ba5 wins.} Nxh2! {20...Rh6? 21. Qe4 Nxh2? 22. Qh4+ and Qxh2 wins for White.} 
  21. Kxh2 {Just to illustrate how difficult the position is, see if you can calculate how Black wins after 21. Bd2.} Rh6!! {And Black wins because of the dual threats of ...Rxc6 and ...Qxf1. Comparatively 21...Qxf1? 22. e6 gives White enough counterplay to force a draw.}
  
  </code></pre>
  <p>Grischuk (White) went 14. Qf3? allowing Ding a game-winning continuation beginning with 14...Bd5, that was however not easy to spot by an unassisted human. After seven minutes Ding played (&quot;blundered&quot;) 14...Rb6 and the game was eventually drawn.</p>
  <p>However: given the complexity of the variation and how hard it is for a human to spot, can you fairly call 14. Qf3 or 14...Rb6 blunders?</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2023-07-28T06:03:24.310Z
Answers.Text: Can't figure out how to add the correct move numbers to the diagram, if anyone can please go ahead and edit the post.
Answers.UserDisplayName: Allure
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2023-07-28T08:33:28.093Z
Answers.Text: There is no way to start at a random number with the replayer as is, to my knowledge.  The only real solution is to put in the entire game and use [startply "x"] beneath the FEN.
Answers.UserDisplayName: Rewan Demontay
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2023-07-28T13:19:19.783Z
Answers.Text: @RewanDemontay, I added the whole game, but the [startply] param doesn't really do it for me? In the PGN the Param 'PlyCount' is mentioned for half moves, but that doesn't work either :-|
Answers.UserDisplayName: IT M
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2023-07-29T00:27:03.737Z
Answers.Text: @ITM It counts by half moves, aka a ply. You put in the move number instead.
Answers.UserDisplayName: Rewan Demontay
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2023-07-28T05:59:32.790Z
Answers.LastActivityDate: 2024-01-31T02:39:07.397Z
Answers.LastEditDate: 2024-01-31T02:39:07.397Z
Answers.UserDisplayName: Allure
Body: <p>Any high-level GM games where somebody makes a big blunder but was in blissful ignorance about how bad the move was until several moves after the blunder?</p>
  <p>EDIT thanks to comment: classical time format, not blitz (where blunders are common)</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2023-07-27T15:11:26.473Z
Comments.Text: You could probably find hundreds of lichess Blitz games, or blunders happening in mutual time trouble.
  
  Are you asking for classical time controls tournament games?
Comments.UserDisplayName: Hauptideal
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2023-07-27T22:30:49.137Z
Comments.Text: @Hauptideal yes pretty much
Comments.UserDisplayName: Chris Sanders
Tags: <grandmaster><master-games><blunder>
Title: Blunders that they didn't realise for some time
ThreadText: # Blunders that they didn't realise for some time
  
  (Asked by: username_0 on 2023-07-27)
  
  Any high-level GM games where somebody makes a big blunder but was in blissful ignorance about how bad the move was until several moves after the blunder?
  
  EDIT thanks to comment: classical time format, not blitz (where blunders are common)
  
  **Tags:** grandmaster, master-games, blunder
  
  > **Comments:**
  > **username_1**: You could probably find hundreds of lichess Blitz games, or blunders happening in mutual time trouble.  Are you asking for classical time controls tournament games?  
  > **username_0**: @username_1 yes pretty much  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_2 on 2023-07-28. Score: 2 | Accepted answer
  
  Of course this has happened, but it depends on your definitions. With the definition that "a blunder is a move that changes the game-theoretic state of the game" (e.g. "draw" to "loss" or "win" to "draw"), then here's an example where both Ding Liren and Alexander Grischuk were blissfully unaware of the blunder until after the end of the game.
  [FEN ""]
  [White "Grischuk, Alexander"]
  [WhiteElo "2759"]
  [Black "Ding, Liren"]
  [BlackElo "2811"]
  [Result "1/2-1/2"]
  [startply "26"]
  
  1. d4 Nf6 
  2. c4 e6 
  3. Nf3 d5 
  4. g3 dxc4 
  5. Bg2 a6 
  6. O-O Nc6 
  7. e3 Rb8 
  8. Nfd2 e5 
  9. Bxc6+ bxc6 
  10. dxe5 Ng4 
  11. Nxc4 Be6 
  12. Qe2 h5 
  13. Rd1 Qc8 
  14. Qf3? Bd5 
  15. Rxd5 cxd5 
  16. Qxd5 Qf5! {Black threatens ...Qxf2+ and mate.} 
  17. f3! {Both Grischuk and Ding Liren saw this far and could not see a refutation of this move.} Qc2! {Black threatens ...Qxc1+, and ...Qf2+ followed by mate.} 
  18. Qc6+! {18.Nbd2? Qd1+ 19. Kg2 Qe2+ wins. White has to move the Queen so that the d2-knight is no longer pinned, and Nf1 becomes possible.} Kd8 
  19. Nbd2 Qd1+ 
  20. Nf1 {If White gets a single free move here, 21. Bd2 intending 22. Ba5 wins.} Nxh2! {20...Rh6? 21. Qe4 Nxh2? 22. Qh4+ and Qxh2 wins for White.} 
  21. Kxh2 {Just to illustrate how difficult the position is, see if you can calculate how Black wins after 21. Bd2.} Rh6!! {And Black wins because of the dual threats of ...Rxc6 and ...Qxf1. Comparatively 21...Qxf1? 22. e6 gives White enough counterplay to force a draw.}
  
  
  Grischuk (White) went 14. Qf3? allowing Ding a game-winning continuation beginning with 14...Bd5, that was however not easy to spot by an unassisted human. After seven minutes Ding played ("blundered") 14...Rb6 and the game was eventually drawn.
  However: given the complexity of the variation and how hard it is for a human to spot, can you fairly call 14. Qf3 or 14...Rb6 blunders?
  
  > **Comments:**
  > **username_2**: Can't figure out how to add the correct move numbers to the diagram, if anyone can please go ahead and edit the post.  
  > **username_3**: There is no way to start at a random number with the replayer as is, to my knowledge.  The only real solution is to put in the entire game and use [startply "x"] beneath the FEN.  
  > **username_4**: @RewanDemontay, I added the whole game, but the [startply] param doesn't really do it for me? In the PGN the Param 'PlyCount' is mentioned for half moves, but that doesn't work either :-|  
  > **username_3**: @ITM It counts by half moves, aka a ply. You put in the move number instead.  
  
  ---
  
  