only_strong_moves vs hikaru

Black chose 19...a6, pushing the a7 pawn to a6. The move does nothing to stop White's immediate threats: the white rook on a5 now attacks the newly created pawn on a6, and the black queen on e5 continues to be vulnerable to a white queen infiltration. Moreover, the move leaves the black rook on c8 completely undefended and does not address the powerful white threats on a7, c5 and d7. By playing a6, Black actually creates a new target (the pawn on a6) while keeping material balance unchanged.

The engine recommends 19...Qc7. Moving the queen off the e‑file eliminates the direct attacks on e2 and g3, and places the queen on c7 where it defends the a7 pawn and eyes the c5 knight. After 19...Qc7, Black keeps the a‑pawn intact, retains the rook on c8, and prepares the tactical idea ...Qb4, pressuring the b2 queen and the d2‑c4‑b3 diagonal. In contrast, 19...a6 loses a pawn, leaves the rook on c8 hanging, and gives White a free tempo to increase pressure. The engine’s line preserves material, improves piece coordination, and neutralises White’s most dangerous threats.

Defend What Is Threatened Before Creating New Weaknesses: Always address the opponent's active threats first; moving a pawn that becomes immediately vulnerable (a6) is a classic missed opportunity. Prioritise piece moves that both defend key squares and create counter‑play, as the queen move Qc7 does.