Von Popiel - Marco, Monte Carlo 1902, how to win as black? In the game: Von Popiel - Marco, Monte Carlo 1902:
why would Black win with Bg1?

Ultimate Blunder

Puzzle

The white player is about to lose the Queen. Does that alone immediately constitute as a loss in that level of Chess play?
The white player is about to lose the Queen. Does that alone immediately constitute as a loss in that level of Chess play?


Well, no. The problem with White position is that he lacks any real counterplay. He has weaknesses he can not defend in the long run, especially pawn at a2, and his piece coordination is not good enough to defend against the might of the queen.

Below illustrative lines prove that:

[Title "Von Popiel - Marco, Monte Carlo 1902"]
[StartFlipped "0"]
[fen "7k/1b1r2p1/p6p/1p2qN2/3bP3/3Q4/P5PP/1B1R3K b - - 0 1"]

1...Bg1 2.Kxg1 Rxd3 3.Bxd3 (3.Rxd3 Bxe4 4.Re3 Qa1 5.Re1 (5.Rxe4 Qxb1+ 6.Kf2 (6.Re1?? Qxe1#) 6...Qxe4-+) 5...Bxf5! 6.Re8+ Kh7-+) 3...Bxe4 4.Bxe4 (4.Re1?? Qc5+ 5.Ne3 (5.Re3 Bxf5!-+) 5...Bxd3-+) 4...Qxe4 5.Ng3 Qc2 6.Rd8+ Kh7 7.h3 (7.a3 Qc5+ 8.Kh1 Qc1+) 7...Qxa2-+


Black will simply take the a2 pawn and win by marching his extra 2 queenside pawns, and there is nothing White can do to stop it. Meanwhile, Queen easily defends any mating attack Rook + Knight conjure up by simply going to the a1-h8 diagonal with the move like ...Qb2 or ...Qc3...