Aaro Jalas sent this amazing game, which transposes to the DDG. It was included in Seltene Gambits ("Rare Gambits") by Anatoli Mazukewitsch.
This is the Tarrasch Defence, Marshall Gambit.
4.cxd5 exd5 5.e4 dxe4 6.d5
Now this has transposed to a well-known DDG position: 1.e4 e6 2.d4 d5 3.c4 dxe4 4.Nc3 c5 5.d5 exd5 6.cxd5.
6...f5!? 7.Bf4
7.Bb5+ Bd7 8.Bxd7+ Qxd7 9.Nh3 Bd6 10.Ng5 Na6 11.O-O Nf6 12.f3 O-O 13.Ne6 Rf7 14.fxe4? Nxe4 15.Nxe4 fxe4 and Black has advantage, Marshall-Spielmann 1908. 14.Bg5!? would have been a natural way to create initiative, according to Mazukewitsch.
7...Bd6 8.Bb5+ Kf7 9.Nh3 Nf6
Maybe 9...a6 could be an improvement: White should find a new square for the bishop, because 10.Bc4 b5 would give Black an important tempo in the queenside.
10.Bc4
10.Ng5+ Kg6 11.Qd2?! Bxf4 12.Qxf4 Nh5 13.Qe5 Qxg5 14.h4 has been played, but 14...Qf4 15.Be8+ Kh6 16.g4 Qxg4 is good for Black.
10...a6
Black wants to prevent 11.Nb5.
11.Ng5+!?
11.a4 h6 12.f3 Re8 13.O-O e3 14.Qd3 Bxf4 15.d6+ Kf8 16.Nxf4 g5 17.Ng6+ Kg7 18.Ne7 Rxe7 19.dxe7 Qxd3 20.Bxd3 f4?! (20...Kf7) 21.Nd5 Ne8? (21...Bd7 22.Nb6 Ra7 23.Bc4 +/-; 21...Nbd7? 22.Nc7 +-) 22.Nb6 1-0, Heikkinen - Davies, corr. 1996.
See games with 11.a4 Te8 and 11...h6.
11...Kg6 12.Ne2
12...h6
12...Bxf4 13.Nxf4+ Kxg5 (14.Qd2 e3) wins according to Fritz!
13.Ne6 Qe7 14.Qb3 Kh7 15.Qg3 Bxf4 16.N2xf4 g5
This is risky, leaving Black's king in an open position.
17.d6
Space for the light-squared bishop, but 17.Nxg5+! hxg5 18.Qh3+ Kg7 19.Qxh8+! Kxh8 20.Ng6+ wins according to Fritz.
17...Qxd6
17...gxf4 18.Qh4 wins.
18.Nxg5+
Editor's note: Incredible 18.h4!! looks like a winning move: 18...g4 19.Ng5+ or 18...Bxe6 19.hxg5 or 18...Nh5 19.Nxg5+ hxg5 20.hxg5. Fritz agrees that it is the best move, giving assessment +2.3.
18...hxg5 19.Qxg5 Ne8
After 19...Rhg8!? 20.Bxg8+ Nxg8, Black gets a knight and bishop for the rook, but queenside is still undeveloped and the king's position is uncertain. Besides, instead of 20.Bxg8+, White can continue the attack with 20.Qh4+ Kg7 21.Rd1, and Black's queen can hardly beat all the threats.
20.Be6 Qxe6!?
White's advantage is decisive; Fritz assesses +1.6.