It is hard to blame Caruana for this move, but he is forcing Karjakin to make the winning combination. [Instead, he could have given up the pawn 36...Bf3
with a playable game.]
37.Rxd5! Without this rook sacrifice, White would be worse.
37...exd5 38.Qxd5 Threatening 39.Qd7 mate.
38...Qc7 Caruana did not have much time and his move loses by force. [The only way to stay in the game was 38...Rd4 39.Qxd4 Qxd4 40.Rxd4 Rb8 White is a healthy pawn up and Black can't win.]
39.Qf5! Rf7 [After 39...Qc6 40.Qh7+ Ke8 41.Qxh5+ Ke7 42.Bd5+- wins.]
40.Bxf7 Qe5 Playing into mate.
41.Rd7+ Kf8 42.Rd8+ [42.Rd8+ Kxf7 (42...Kg7 43.Qg6# ; 42...Ke7 43.Qd7# ) 43.Qh7+ Ke6 44.Qd7# ] 1-0