|Chessical: MacDonnell pays very actively after the very rare <7.c4> to engineer a King-side attack. For Mackenzie's method of play as white in this position see: Mackenzie vs G Medley, 1862|
Despite MacDonnel's obviously aggressive intent, he misses some promising opportunities.
<15.Nxc6> there was no need to rush to exchange this Knight, <15. a3> or <15. Re1> could be considered to continue building up the position.
Mackenzie plays calmly and accurately, and perhaps the only move he can fairly be criticised for is <16...Qd7?!>.
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This permits the promising temporary pawn sacrifice:
<17. d5!> Ne7 18. Bd4 Nexd5 19. Bxh7+ Nxh7 20. Nxd5 Rfd8 21. Rh3.
<16....Re8> prevents this idea, it would have allowed the Rook to take the Bishop on e3 with the follow up pin of Bc5.
<23.Ne2?> is far too slow, and immediately loses control over <d5>. The straightforward <23.g4> would have been better, although the position would remain balanced.
MacDonnell probably rejected <22. Bxh6!?> as it was no more than a draw. For instance:
<22...gxh6> 23. Rxh6 Kg7 24. Rxf6 Rh8 (not 24... Kxf6? 25. Ne4+!) 25. Qg4+ Kf8 = (but not <25... Kxf6??> 26. Ne4 and mate.
Mackenzie missed <25...Nxf5>. At this point, MacDonnell probably would still have drawn if he had simply put his Bishop on <f2>. Instead, obviously believing he was striking the winning blow, MacDonnell incorrectly sacrifices his Rook on <h6> with the simple mate threat of Bh6.
Mackenzie's <26..N(e)g8> completely refutes the idea, and the game is over.