1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g2g3  3... d7d5  4. f1g2  4... b8c6  5. g1f3  5... a8b8 A very rare move. According to my database, it is just the 10th choice for Black in this position. Caruana usually shows interesting ideas in the opening. 6. c4d5  6... f8b4 Already a new move. 7. b1c3  7... e6d5  8. c1g5 White has many options but decides to exchange the bishop for the knight, which will more or less force Black to do the same. 8... h7h6  9. g5f6  9... d8f6  10. e1g1  10... b4c3 The pawn on d5 was attacked, and it's a good idea to capture the knight.