Solution to the historical riddle Botvinnik vs Bronstein 1951: Bronstein could have drawn

Bronstein could have drawn

This was  a very complicated riddle that also touched the rules of chess. Charles Sullivan had immediately pointed out White has many ways to reach a won position but in many lines he fails to mate the enemy king in 50 moves or less which means that Black can draw according to the 50-move-rule.

But what was Bronstein's last and decisive mistake? Was it 52...Nc8?, a move that loses with and without the 50-move- rule, whereas 52...Ne7 draws as Jan Timman had shown earlier.

Many lines in the analysis of this endgame lead to endgames with two bishops against knight, which are theoretically won but not with 50-move-rule.

This leads to a question related to chess history: which version of the 50-move-rule was used in 1951? Nowadays, FIDE decrees that the 50-move-rule always applies, with no exception and no matter whether certain positions will lead to mate in a given number of moves. However, in the past the rule was applied differently. Fortunately, Harold van der Heijden was able to shed some light on this issue. He writes:

"The ending was considered a draw from 1851 (Horwitz & Kling fortress) until the 1980’s when Thompson and Comay independently used a computer to prove that the ending is a general win.

Then about the rules.

In a book that is pretty close to the 1951 date of the game, André Chéron (Lille, 1952): Nouveau Traité Complet D’Échecs – La Fin de Partie, dedicates a chapter (page 741) to 50 move plus endings ("Les Finales Exigeant Plus de 50 Coups"). He mentions BR vs R, 2N vs P and R + Pa2 vs B (black squares) + Pa3. Of course, he does NOT mention 2B vs. N but for a certain limited and clearly defined number of positions, he proposes to change the 50-move-rule, and to allow the side which makes winning attempts 100 moves in which no pawn is moved and no piece or pawn is taken before the game is declared drawn.

So it seems that Chéron PROPOSES a new rule in 1952 …. which indicates that such exceptions did not exist?"

Thus, Charles Sullivan and Zoran Petronijevic had to work very hard to prove not only that White could win but also to prove that White can win within the limits of the 50-move-rule.

After burning a lot of midnight oil Zoran Petronijevic reached the following conclusions:

• The adjourned position after 41...Kg6 is won for White. White wins with 42.Bb1, which was analyzed by Flohr and Botvinnik, or with 42.Bc2.
• 42.Bd6?, the move White sealed, is a clear mistake and leads to draw.
• 43…Kf6 is not a mistake but 43…Na7 leads to an easy draw. We should notice that Bronstein in his notes to the game claims that he looked at this move during his analysis of the adjourned position but after the resumption of the game got confused and did not play it.
• 44.Bg3 by White is a normal move.
• 44…fxe4 by Black is not a mistake. Apart from the move he played in the game, Bronstein had other moves to draw the game. For instance, 44…Ne7 (though Kasparov thought that this move loses). 44….h5 and 44…h6 lead to theoretically lost positions though in practice White would not have won these positions because of the 50-move-rule which was valid in 1951. We can thus conclude that these moves might also have led to a draw.
• 45…h6 is a mistake and leads to a theoretically lost position. After 45…h5 the position is even.
• 46.Bf4 is a mistake but 45.exd5 leads to a win. White must be careful to avoid positions that allow Black to draw because of the 50-move-rule. Charles Sullivan helped a lot to find proper winning lines but it is hard to say whether the position is definitely winning.
• 46…h5 is the best move, but 46…dxe4 also draws because of the 50-moves-rule.
• 48…Nab8 leads to even play. Kasparov erred when he gave 48..Ne7 as losing.
• 50.Bf5 is a normal move and does not deserve the exclamation Kasparov gave the move.
• 50…Ne7 draws – contrary to Kasparov’s opinion.
• 52…Nc8 is a decisive mistake. After 52…Ne7 (which as far as I know was found by Timman) the position is even.

Here's the complete analysis of this difficult and historically important ending.

Links

• The historical puzzle: Botvinnik vs Bronstein 1951
• How sound was the endgame Spielmann-Rubinstein?
• Riddle solved: Spielmann could have drawn!
• Could Petrosian have held against Fischer?
• Petrosian could have held!
• The old riddle of Fischer vs Taimanov
• Riddle solved: Fischer was winning
• The old riddle of Botvinnik vs Fischer
• Riddle solved: Fischer could have won
• Historical riddle: could Kramnik have defeated the computer?
• Kramnik could have defeated Fritz