Gukesh was probably out of book as well, since he thought for nearly 20 minutes before playing this.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... a7a6  4. b5a4  4... g8f6  5. e1g1  5... f6e4 The Open Variation of the Ruy Lopez is a defense with an excellent reputation and played from time to time at the elite level. 6. d2d4  6... b7b5  7. a4b3  7... d7d5  8. d4e5  8... c8e6  9. d1e2  9... f8e7  10. f1d1  10... e8g8  11. c2c3 [%c_effect c3;square;c3;type;Interesting;persistent;true] 11.c4 is played in the vast majority of the games. Moving the pawn only one square forward is a fresh idea that quickly takes the game out of well-known paths. 11... e4c5 Narayanan took more than 10 minutes to play this, indicating he was surprised by Gukesh's previous move. 12. b3c2  12... e6g4 