comment: The knight gets ready to attack the bishop after Nd2.
context: 1. c2c4 The most natural move. 1... g8f6 The knight is vulnerable on f6, as we will see in the game. In addition to the potential capture with the bishop on a1, another problem is that White can advance e4-e5, attacking it. 2. g1f3  2... b7b6  3. b2b4  3... c7c5 Caruana isn't afraid of losing the h-pawn. 4. a1e5 A very subtle and interesting move. Keymer wants to close the diagonal before capturing on f6. 4... d7d6  5. e5f6  5... e7f6  6. b1h7  6... h8g6 The game becomes sharp. Black has problems with the king, as it has no safe place to go to. But Black has good control of the center, and White also needs some time to castle on the kingside. 7. e2e3 Accelerating development. 7... c5b4  8. f1e2 White intends to castle, and Black has a problem with the king. 8... c8c5 The wrong plan. 9. h1g3 An accurate reply. 9... b8c7  10. d2d4  10... c5a5  11. c1c2 A safe move. 11... a8c6  12. d1e1 Black failed to solve the king problem and is now strategically lost. White can play with c5, with d5, with h5, which are all interesting plans. Meanwhile, the black pieces lack harmony. 12... a5a3  13. h2h4  13... c6a4  14. c2c1 Surrendering the a2-pawn isn't really necessary, but it's also a good choice. 14... a7a5  15. h4h5  15... g6e7 Black's position is simply horrible—everything is wrong. There are so many tempting moves for White that it's even difficult to choose just one. 16. d4d5  16... a3a2  17. f3d4  17... c7d7  18. c1a1 Trying to exchange Black's only active piece. 18... a2d2  19. h5h6  19... g7h6  20. e2h5  20... d2d4 There's nothing to recommend. Caruana tries to complicate the game, but his fate is already sealed. 21. e3d4  21... a4b3  22. h7d3  22... a5a4 With such an advantage, Keymer plays the remainder of the game safely. On every move, he has good alternatives. 23. f1b1  23... e7c8 