Instructive End-game Tactic (Played at Chess.com)

I felt like I played a pretty good game, but I blundered at the end. My opponent played the sharp 26.Nc8. I resigned after this move because either I lose my rook on b6, or I get checkmated.

[Event "Let’s Play!"] [Site "Chess.com"] [Date "2016.11.29"] [White "gary5daniels"] [Black "TERLIZZI"] [Result "1-0"] [ECO "C47"] [WhiteElo "1709"] [BlackElo "1507"] [TimeControl "1 in 2 days"] [Termination "gary5daniels won by resignation"] [CurrentPosition "2N3k1/5ppp/1r6/1p6/8/1b6/3R1PPP/6K1 b - - 0 27"] 1.e4 Nf6 2.Nc3 e5 3.Nf3 Nc6 4.d4 exd4 5.Nxd4 Nxd4 6.Qxd4 d6 7.e5 dxe5 8.Qxe5 Qe7 9.Qxe7 Bxe7 10.Bf4 c6 11.Bd3 Be6 12.O-O O-O 13.Ne4 Nd5 14.Bd6 Bxd6 15.Nxd6 Rab8 16.Bc4 a5 17.Bxd5 Bxd5 18.c4 Be6 19.b3 b5 20.cxb5 cxb5 21.Rab1 Rfd8 22.Rfd1 a4 23.Rb2 axb3 24.axb3 Rb6 25.Rbd2 Bxb3 26.Nc8 Rxd2 27.Rxd2 1-0'/>