Chessical: As Lasker said - "any defence of the <g> pawn but this"<4...Qf6?!> to protect the K-side (4..g6 or Bf8).
Chigorin fell victim to a Mieses speciality variation which proved to be too involved for him to analyse out correctly at the board.
Mieses had prevously used this variation against: Teichmann, Cohn (twice), Marshall and Mortimer (twice) in the period 1895 - 1906, which illustrates the difference in dissemination and study of opening variations in those days compared to our digital age.
<10...Na5?> described at the time as the decisive error.
He had to play <10...Qf2> which threatens <Nd4> Thus, <11.c3 Nf6 12.d4 Bxd4 13.Rf1 Nxe4 14.Qd7> (Lasker). After <13...Nxd4!> play is very complex, but White appears to have an advantage, e.g. <14.Be3 Qf5>
If <15...Ne7 16.Bg5>, and if <15...g6 16.Bh6+ Nxh6 17.Qg7+ Ke8 18.Nf6+ Kd8 19.Qd7> mate.