The opening is over and Nakamura has a few weaknesses to worry  about. But the c4-pawn is also a strength that cramps the white bishop and secures an excellent outpost for the knight.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... d7d5  4. b1c3  4... d5c4  5. e2e4  5... b7b5 A very fresh line which was tried on a couple of occasions by Caruana. Apparently Nakamura liked  the idea and decided to give it a try. 6. e4e5  6... f6d5  7. c3b5  7... d5b6  8. a2a3  8... b8c6  9. c1e3  9... c6a5 Played after some hesitation. The knight is  protecting the c4-pawn and is ready to jump on b3 at the right moment.