So sad.

The Gunderam defense is often a hard nut to crack for the attacker. I found this last weekend during an online blitz game, where I failed to find the correct continuation.

I was confident when my opponent deviated from the normal Gunderam defense 6...e6 7.g4 and 6...c6 7.g4 by playing the "inferior" 6...Nbd7, attacking my knight on e5 right away. My book "Attack with the Blackmar Diemer" had listed the line as (+=), however, but now it seems this might have been more than a bit too optimistic.

1.d4 d5 e 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 Bf5 6.Ne5 Nbd7
This is where things start. "Normal" black moves are 6...e6 and 6...c6

7.Qf3 e6
Other black moves are clearly inferior. 7...g6 is punished by 8.Qxb7 (+=) whilst 7...Bg6 8.Qxb7 is even worse.

8.Qxb7 Nxe5

a/ 8...Rb8 9.Qxa7 ( diagram ) is an alternative

...a1/ 9...Bc5 10.dxc5 Nxe5 11.Bb5+ (+=)
...a2/ 9...c5 10.Nb5 (+=)
...a3/ 9...Bb4 10.Nc6 (+)
...a4/ 9...Be4 10.Nxd7 (+=)
...a5/ 9...Ne4 10.Nxd7 (+)
...a6/ 9...Be7 10.Nc6 (++)
...a7/ 9...Bd6 10.Nc6 (+)
...a8/ 9...Ra8 10.Qb7
......a8a/ 10...Rb8 11.Qf3 (=)
......a8b/ 10...Nxe5 11.dxe5 (=)
...a9/ 9...Nxe5 transposes below

9.dxe5
The starting point of our analysis. White optically looks better, but that is not the case.

b/ 9...Rb8 10.Bb5+ Nd7 11.Qxa7 ( diagram )
Also possible is 11. Bxd7+ Kxe7 12.Qxa7 but 12...Qh4+ 13.g3 Qc4 gives black an equal game as the rook on b8 cant be taken

...b1/ 11...Ra8 12.Qd4 (+=)
...b2/ 11...Bb4 12.Bxd7 Kxd7 13.00 (+-)
...b3/ 11...Rxb5 12.Nxb5
......b3a/ 12...Bc5 A killer move 13.Nxc7+ ( 13.Qxc7 is not possible because of 13...Qh4+ )
.........b3a1/ 13...Kf8 14.Qa8 Qxa8 15.Nxa8 Be4 16.Nc7 Bxg2 17.Rf1 Bxf1 18.Kxf1 (=)
.........b3a2/ 13...Ke7 14.Qa5 (+=)
......b3b/ 12...Qh4+ 13.Qf2 Qb4+ 14.Nc3 Bc5 15.Qf4 (=)
......b3c/ 12...Bb4+ 13.c3 Bc5 14.Nxc7+ Kf8 15.Qa8 (=)

c/ 9...Nd5 10.Qc6+ (++)

d/ 9...Nd7 10.Bb5+ Rb8 transposing to the line (b) above

The alternative continuation in line (b) 10.Qc6 Rb8 11.Bb5 Rb6 12.Qf3 does also not offer anything for the attacker, since 12...Rxb5 13.Nxb5 Nxe5 is equal.

So it seems the "inferior" 6...Nbd7 in the Gunderam defense gives black an equal game, provided the defender finds the killer moves 11...Rxb5 12.Nxb5 Bc5.

It is so sad to realise Blackmar Diemer gambit does not always lead to a forced win...