context: 1. f2f4 The most natural and also the best move, opening the diagonal for the bishop and attacking the a7-pawn. No wonder it was played in all four games of the round. 1... a8b6  2. a1b3  2... f7f5  3. e2e4 Judging by the other games, this is a kind of \"theoretical line\" from this starting position. The computer doesn't approve of this move. 3... f5e4  4. e1e4  4... g8d5 A logical move, improving the position of the bishop and leaving room for the queen. However, the bishop can be attacked by the knight after Ne3. 5. e4e1  5... h8g8  6. g1f2  6... f8g6  7. f4f5  7... g6f4  8. f1e3  8... e7e5 A difficult decision, allowing White to capture the valuable bishop. An option is to move it to f7 or c6. 9. e3d5  9... f4d5  10. g2g4 Opening the diagonal for the queen and securing the pawn on f5. 10... c7c6  11. b1a1 A subtle move, preparing a4-a5. 11... d5f4 The knight stabilizes itself in a comfortable square, making way for the queen.. 12. a2a4  12... a7a5 It's necessary to stop a4-a5. 13. b3c5 White has a few tempting moves: 13... b6d5  14. c5e4 The knight is ready to go to d6. There are three ways to cover this square, and all are reasonable. 14... g8f8  15. g4g5 A very risky move, destabilizing the pawns on the kingside. 15... d8b6 Both 15...Be7 and 15...Bc7 are good for Black. 16. f2b6  16... d5b6  17. f5f6  17... c8c7 Covering the d6-square. 18. h1g1  18... d7d5  19. f6g7  19... f8b4 An excellent attacking move. 20. e4c5 The knight goes to b3 in order to protect the king. 20... d5d4 This isn't the best way to develop the initiative. 21. c5b3  21... e8e7  22. e1e4  22... b6c4 This leads to trouble. Both 22...Nbd5 and 22...Qd6 preserve equality. 23. g1f1 An almost lethal repositioning. The queen keeps an eye on the two knights, one of which can be a target after c2-c3 and the other can be captured by the rook or even the queen, as we will see shortly. 23... c4d6 The only defense. 24. c2c3  24... b4c4  25. f1c4  25... d6c4 The endgame is complicated, but Black is no longer worse. 26. b3d4  26... c4d6 Black wins the exchange now. 27. e4f4  27... e5f4  28. d1b3  28... c7d7 Careful defense by Caruana. 29. g7g8q  29... b8g8  30. b3g8  30... e7e1  31. c1c2  31... e1a1  32. g8h7  32... d7e7  33. h2h4 The fatal mistake. 33... a1h1  34. d4f3  34... h1h3 The knight has to move, and Black wins easily. 35. f3e5  35... f4f3  36. c2d3  36... e7e6 