KEG: The Tournament Book notwithstanding, this looks like a game Showalter should have won.
Tchigorin had little success against Showalter's Stonewall formation, and his 20...e5 was not good.(20...Ngh6 seems best).
After 21. dxe5 fxe5, Showalter had fine winning chances with 22. g5. But he let Tchigorin off the hook by exchanging Queens with 22. QxQ. 23. fxe5 was also weak (23. Ng3 was better), as was 24. Nf4 (24. g5 still gave him a small edge). Tchigorin then seized his chance, and with 25...Ne4 had if anything the better game.
After weathering the storm, one would have expected Tchigorin to take control. Instead, he erred with 28...Kg8 (instead of 28...h6)
What follows is hard to explain. Showalter could have solved all his problems with the obvious looking 32. Be7. Instead, he delayed this move, playing the inferior 32. Rad1 first. Now Tchigorin had good chances with 32...h6 or, more to his style, 32...RxB, sacrificing the exchange. Tchigorin then missed another chance (under slightly less favorable circumstances) to sacrifice the exchange on move 33. Of all people, one would have expected Tchigorin to have capitalized on this chance!
Tchigorin's 34...h6 (too late!) was poor (he again should have taken Showalter's Bishop and gotten some initiative by sacrificing the exchange).
Then, after missing three chances to sacrifice the exchange when it might have been in his interest to do so, Tchigorin blundered with 36...Rh7 (36...Nxh4+ being best) and lost the exchange for nothing.
Showalter could probably have won with a simple exchange sacrifice of his own with 38. RxN, but his 38. Kg3 appears more than adequate to win.
Tchigorin's 39...g5 could have been punished with the immediate 40. BxR+, but--once again--Showalter's move (40. hxg5+) though inferior was good enough to win.
After Showalter's 44. Rd4, the Tournament Book says that, though up the exchange, Showalter had no way to win. This seems wrong. With 48. Ne6, Tchigorin seems lost to me [Fritz rates the position +6.79 for Showalter].
But instead of playing 48. Ne6 (or 50. Ne6 for that matter), Showalter engaged in a series of useless checks.
Showalter did not play his Knight to e6 until move 55, by which time Tchigorin had set up a counterattack. Even here, instead of 55. Ne6, Showalter had a win with 55. Kf2.
The win was probably gone after 55. Ne6. It was definitely gone after 56. Kf2 (one move too late!).
A series of missed opportunities by Showalter, and a lucky escape by Tchigorin, who was outplayed for most of the game but exploited his chances in the finale.