[%c_highlight c6;keyPressed;none;opacity;0.8;square;c6;persistent;false,d5;keyPressed;none;opacity;0.8;square;d5;persistent;false] This move is only the third most popular choice for Black, but it has been played by Firouzja before. Advancing the pawn to c5 is generally a difficult decision: on the one hand, Black gains the c6-square for a bishop or knight; on the other, the d5-square becomes available for the white knight.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... g8f6  4. e1g1  4... f6e4  5. d2d4  5... e4d6  6. b5c6  6... d7c6  7. d4e5  7... d6f5  8. d1d8  8... e8d8 Vachier-Lagrave from time to time still tries to defeat the Berlin Defense with the endgame that so exasperated Kasparov in his 2000 match against Kramnik. At the super-GM level, Black has certainly defended well, but I have the impression that amateur chess players underestimate the difficulty of playing this endgame with Black. 9. h2h3  9... c8d7 [%c_arrow d8c8;keyPressed;none;from;d8;opacity;0.8;to;c8;persistent;false,b7b6;keyPressed;none;from;b7;opacity;0.8;to;b6;persistent;false,c8b7;keyPressed;none;from;c8;opacity;0.8;to;b7;persistent;false] Taking the king to c8 and then playing b6-Kb7 is one of the most combative plans for Black. 10. b1c3  10... h7h6 An important move to prevent Ng5. 11. b2b3 White prepares the development of the bishop on b2—so far, all his moves are very natural.