1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 Bg4 6.h3 Bxf3 7.Qxf3 c6 8.g4 e6 9.g5 Nd5 10.Bd3 Be7 11.h4 Qb6 (diagram)
I had played this opponent before, so I guess he was well prepared to play this line. I played 12.Bd2 Nd7 13.0-0-0 and I found myself in a lost position after 13...Qxd4. With two pawns down, I realised I had nothing - and indeed I went down the drain quickly.
So what should I play here ?
12.a3 is countered by 12...Nd7, and after 13.Bd2, white has lost one move compared to the immediate 12.Bd2.
12.Nxd5 cxd5 13.c3 is good for black, I think black can castle safely as the white queen cannot attack anymore via square e4, eg 13...0-0 14.h5 Nd7 (=+)
12.Rf1 is also no good as the simple 12...Qxd4 13.Qxf7+ Kd7 14.Qf2 Qxf2 leaves beaves white one pawn down without compensation.
So the only option for white to mplay for an advantage is 12.Bd2 (diagram), as I played in my game.
Black's options include
a/ 12...Qxd4 13.Nxd5
...a1/ 13...Qxd5 14.Be4 Qc4 15.0-0-0 Qxa2 16.Bc3 (=) (diagram below)
...a2/ 13...cxd5 14.Bc3 (+=)
...a3/ 13...exd5 14.0-0-0 (+=)
b/ 12...Nd7 13.Nxd5
...b1/ 13...cxd5 14.0-0-0 (=)
...b2/ 13...exd5 14.0-0-0 (+=)
d/ 12...Nb4 13.Be4 (+=)
e/ 12...0-0 13.Qe4 g6 14.h5 (+)
f/ 12...f5 13.gxf6 (+=)
h/ 12...Na6 13.Rf1 (=)
The position in line a1 is interesting. White has sacrificed half of his army, whilst black only has developed his queen.
White can unleash dangerous attacks in this line. Black's best try is 16...Nd7 17.Bxg7 Rg8 18.Rxd7!!! (diagram) with a complicated game.
So dont dispair if your opponent makes great moves - the Blackmar Diemer gambit contains winning sacrifices in every line !