How Knight Promotions Win Chess Games

Can underpromoting a pawn to a knight help you win in chess? Consider recent wins by grandmasters such as Levon Aronian, Hikaru Nakamura, and Maxime Vachier-Lagrave and how decisions on knight promotion affected the outcome of those games. On the losing end of this surprising maneuver were GMs Wesley So, GM Le Quang Liem, and again So, respectively.

Is promoting a pawn to a knight even legal? Doesn’t a promotion automatically result in a queen? (Which move—an en passant capture or an underpromotion, particularly to a knight—is harder for a novice player to accept is legal? )

Of course, we know that underpromotion is legal. It makes a passed pawn even more dangerous because it can promote to any piece and the advice by Aron Nimzowitsch even more sage: "A passed pawn is a criminal which should be kept under lock and key. Mild measures, such as police surveillance, are not sufficient.”

• Winning With Underpromotion By Aronian
• Missed Opportunity Against Nakamura
• So Stunned Again By Knight Promotion

Winning With Underpromotion By Aronian

Just last month at the New in Chess Classic, Aronian won a rapid (15|10) match against So on the first day of the quarterfinals by underpromoting to a knight. Although So saw a mating threat with Aronian’s pawn about to promote, he missed the danger of an underpromotion to a knight that instantly placed his king in check. If Aronian had instead promoted to a queen, So could have ended the game immediately with 33…Qg5#. In contrast, the underpromotion quickly won the game for Aronian as So resigned after four more moves.

During the game, Aronian was concerned that “auto-queen” had been selected in his settings and even tweeted after the game his anxiety about promoting the pawn. Nevertheless, he managed the underpromotion without any difficulty. Fair warning: Make sure your settings don’t prevent you from making an underpromotion in games with fast time controls.

Missed Opportunity Against Nakamura

A day after the Aronian-So match, the second day of the quarterfinals of the New in Chess Classic also was the opportunity for a stunning underpromotion, again to a knight. However, Nakamura successfully won his rapid game (15|10) and match against Le, who missed the potential for the underpromotion on the 28th move (that is a continuation of the variation that begins with 24.Qxe8! instead of 24.e4, the move that Le made, and is followed by 26.Rc2!!).

In the Game of the Day analysis, GM Dejan Bojkov shows how Le’s blistering attack that had forced Nakamura’s king into the open could have led to an inevitable mate if the passed h-pawn had been advanced and promoted to a knight. (Bojkov speculates that Le considered a promotion only to a queen and rejected this idea. The pawn incidentally dies on h7 as Nakamura demonstrates his defensive skills and wins the game.) Lesson learned: When the enemy king is boxed in as Nakamura’s monarch was (observe that the black king cannot move after 24…Kd6), evaluate how an underpromotion to knight can suffocate the king.

A passed pawn is a criminal which should be kept under lock and key.
—Aron Nimzowitsch

So Stunned Again By Knight Promotion

Several months before the New in Chess Classic was held, the Airthings Masters pitted 12 top GMs in a rapid (15|10) round-robin. In the quarterfinals, So fell victim again to an underpromotion, this time by Maxime Vachier-Lagrave. Protected by a bishop and rook, So’s king looked safe until MVL’s pawn advanced to f1. Instead of becoming a queen, which would have immediately been attacked by So’s major pieces around the king, the pawn was promoted to a pesky knight that instantly placed the king in check. 

MLV’s unrelenting attack around the king led So to blunder in a few more moves and sealed the fate of the game: A win for Vachier-Lagrave—set up by a crucial knight promotion. What to remember? Using a knight promotion to check a king can gain a valuable tempo. 

Are you surprised that underpromoting a pawn to a knight can be so decisive? I’m still waiting on the opportunity to make that move in a game to determine its outcome. However, from these games, I have learned something important: I’ve unselected “auto-queen” in my online settings.

Now it’s your turn. Please add your comments below. Have you promoted a pawn to a knight in a game? Has an opponent balked when you underpromoted? Do you still have “auto-queen” selected in your settings?