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 