1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 Ne7 5.a3 Bxc3+ 6.bxc3 b6 Black's main alternative to the ...c5 lines, the idea being to solve the Bc8 quandry.
7.Qg4 Ng6 8.a4 A rare continuation though. 8.h4 is the usual path.
8...Ba6 9.Bxa6 Nxa6 10.h4 h5 11.Qe2 Nb8 12.Bg5 Qd7 13.a5 Nc6 14.axb6 cxb6 15.Qf3 By playing the queen to f3 instead of Nf3, White keeps the h5 pawn under fire, making kingside castling impossible.
15...Nge7 16.Ne2 0-0-0 Very risky and putting the king under fire. [16...Na5 was certainly worth consideration, though if it does not work out, then something earlier will need to be found. 17.0-0 Nf5 18.Nf4 g6 19.Bf6 Rf8 This may not look great for black, but the alternative is queenside castling which came under heavy attack in the game.]
17.Nf4 g6 18.0-0 Kb7 19.Rfb1 Rb8