comment: Controlling the promotion of the d2-pawn.
context: 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. 11. b2c3  11... e8g8 An interesting position resulted from Black's experiment in the opening. By exchanging two pairs of minor pieces, Black's position is less constrained than normal in queen's pawn positions. However, it's important to note that White has an extra pawn in the center (d4 and e2 versus d5), which is a strategic advantage that can become considerable if the c4 or e4 move arrives at the right time. Overall, it can be said that the position is close to equality, but accurate play is still required on Black's part. 12. f3d2 Threatening the pawn on d5 and providing support for future breaks on e4 or c4, which are the basis of the white plan. 12... c6e7 The knight returns to defend the pawn on d5 and also makes it possible to advance the pawn to c6 (which allows the knight to be repositioned later) or even to c5, as will happen in the game. The problem with this move is that it makes it easier for White to advance a pawn to c4 or e4, due to the knight's temporarily passive position. 13. e2e3 Preparing the c3-c4 advance, one of White's plans. Perhaps it would even be better to play the other possible plan, which is to advance the pawn to e4, either now or after 13.Qa4. 13... c8e6 The bishop is developed while keeping an eye on c3-c4. 14. d1a4  14... a7a6  15. e3e4  15... c7c5 Played after lengthy deliberation, but this leads to trouble. 16. a4a3 An unpleasant reply. 16... b7b6  17. a1b1 White decides to make an improving move before capturing on c5, since Black cannot take on d4. But it's not clear whether 17.Rab1 is the most useful move. 17... f8e8  18. d4c5  18... d5d4 A very difficult choice. 19. c3c4 Another tough choice, now for White. This move allows Black to equalize. 19... f6g5 an important move, attacking both the knight and the pawn on c5. 20. f1d1 The alternatives are no better. 20... b6c5 The game remains equal after this move, but it's not easy to play with Black. 21. f2f4  21... g5h5  22. f4f5  22... b8b1  23. d1b1  23... h5e2 Very good play by Caruana. 24. f5e6  24... e2d2  25. e6f7  25... g8f7  26. a3c5 The computer indicates equality in this position, but don't be fooled: Black has to play several forced moves in a row. 26... f7g8 Removing the king from the dangerous f-file. 27. b1f1  27... g8h7 The only move. 28. c5e5 A good try, pinning the knight. 28... d2e3  29. g1h1  29... d4d3 Caruana continues to find the only moves. 30. g2h3  30... d3d2 