1. e2e4  1... e7e5 A bold decision. In general, the Petroff is a very safe opening and the best choice Black has to try to keep solid and hopefully make a draw. Still, I might have chosen something else. Caruana played the Petroff himself some years back, at the 2018 World Chess Championship and had that level of preparation. Nepo did this too, of course, but I think Caruana did it better, and his Petroff has looked like the better prepared and better understood one over the years. Against any other opponent, I'd think the Petroff would be an obvious choice. Here, I don't know. 2. g1f3  2... g8f6  3. f3e5  3... d7d6  4. e5f3  4... f6e4  5. d2d4  5... d6d5  6. f1d3  6... f8d6  7. e1g1  7... e8g8  8. c2c4  8... c7c6 All of this is today's modern mainline. In an earlier round, Rapport chose Qb3, which is more or less a known draw, though he went off the deep end and ended up losing. Caruana chose a more challenging move. 9. f1e1  9... c8f5  10. d1b3  10... d8d7  11. f3h4 The first new move of the game, and I think a very dangerous one in practice. Nepo had to know he would be walking into some kind of preparation, but one has to admire his confidence. 11... f5e6 Nothing else makes any sense. 12. b3c2  12... b8a6 This move looks obvious enough, but I actually think it becomes difficult to fix the knight later on once it is frozen in place with a3. 13. a2a3 Of course. 13... f7f5  14. c4d5  14... c6d5  15. b1c3 Caruana was still blitzing. The machine insists on equality, but I think Black is under some pressure to figure out how to fix his pieces. 15... a8c8  16. f2f3 In my opinion, the hardest pieces of practical preparation to face are the ones where you have to sacrifice material. I think it's much easier if an opponent sacrifices a piece—you just calculate until you see a line that does not lose. But when the only way to equalize is to give material for long-term compensation... I almost never see a human get this right. The computer still insists Black is totally fine, but I think his task is more or less impossible in human terms. 16... d6e7  17. g2g3  17... e4d6  18. c2a4  18... e7f6  19. a4d7  19... e6d7  20. c3d5  20... f6d4  21. g1g2 Be3 was fine too, but I prefer Caruana's choice. More pieces should remain on the board. Now, I've always believed that it is very rare for someone to be slightly better based on piece activity in a symmetrical pawn structure. It is almost always much better or very close to equal. Here, it is much better. Black is facing too many threats. That said, White needs the utmost precision as one mistake will immediately see the game fizzle to sterile equality. 21... c8e8 Ne7+ was threatened, and this was the only move not to lose the game immediately. 22. c1f4  22... a6c5  23. d5e7  23... g8f7 Now, this is a perfect example of what I was saying. There really is no slightly better option for White in this position with a mostly symmetrical structure. The best move is more or less winning, and the second-best move is just about a draw. 24. d3f5 This lets the opportunity slip. White's route to victory was narrow and incredibly difficult, but it was there. 24... d6f5  25. h4f5  25... d7f5  26. e7f5 This position looks so tempting for White from afar. Black is a pawn down, facing massive threats. But somehow he just barely holds together. 26... e8e1  27. a1e1  27... c5d3 Black is just in time to hold. 28. e1e4  28... d4b2 Black is out of danger. The absolute worst-case scenario I could imagine for him is a 3 vs. 2 endgame on the kingside, which would be unpleasant but still a draw. 29. f4e3  29... b2a3  30. e3a7  30... f8a8  31. a7d4  31... a3f8 The rest of the game was a formality. Caruana came very close to blowing the tournament open, showing excellent preparation, but he did not quite manage to see it all the way through when a very, very difficult chance was given to him. Nepo remains a full point in the lead, and thanks to wins from the struggling Radjabov and Firouzja, it seems Caruana is the only player for him to worry about once again. Surviving this game was a huge deal. 32. e4e2  32... g7g6  33. f5e3  33... a8d8  34. d4b6  34... d8d6  35. e3c4  35... d6c6 