Wild Bill: <Marmot: <Early pawn grabs are usually risky. . . .>>
Epishin played this position through eight moves once before. His opponent castled instead of sacrificing the pawn as Nakamura did.
I don't know Nakamura's habits, but he probably knew of the game and prepared the improvement.
The game is not on ChessGames:
[Event "Solsona op 3rd"]
[White "Barrientos Chavarriaga,Sergio"]
1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 a6 5.Bd3 Bc5 6.Nb3 Be7 7.Be3 d5 8.exd5 Qxd5 9.0-0 Nf6 10.c4 Qc6 11.Nc3 Nbd7 12.Be2 0-0 13.Rc1 Rd8 14.Qe1 Qc7 15.c5 Ne5 16.Bf4 Nf3+ 17.Bxf3 Qxf4 18.Ne2 Qg5 19.Ned4 Nd5 20.c6 Bf6 21.Qa5 bxc6 22.Nxc6 Re8 23.Nc5 Bxb2 24.Rc2 Bf6 25.Ne4 Qf4 26.Nxf6+ Qxf6 27.Nb4 Bb7 ½-½