1. e2e4  1... e7e5  2. g1f3  2... g8f6 Caruana switches to the Petroff after the painful loss that he suffered in Norway earlier this year. 3. b1c3 Nakamura prefers to stay clear of the main lines. Just like in Norway, he has prepared something nasty for his opponent, but this time in the Four Knights. 3... b8c6  4. d2d4  4... e5d4  5. f3d4  5... f8b4 