KEG: A missed chance by Pillsbury.
Pillsbury was famous for blowing away opponents when he had the White side of the Queen's Gambit Declined, especially with his 4. Bg5 variation. Showalter had the temerity to take on Pillsbury in this line, but instead of waiting for Pillsbury's attack to rip him up, followed what the Tournament Book called the philosophy that "attack is often the best defense" and went for the jugular instead. Showalter's methods here may not stand up to close analysis, but he certainly made the game entertaining for the spectators of 1899 and of today! And Showalter's tactics succeeded in this game to the extent that he was able to take advantage of a couple of Pillsbury errors and obtain a draw.
Showalter signaled his aggressive intentions with 18...Re6 (rather than the perhaps theoretically better 18...Bg4). More importantly, after Pillsbury's 19. f5, Showalter crossed the Rubicon and committed himself to a do-or-die attack with 19...Rh6. Fritz says this loses and that Showalter should have played 19...Re5. But I'm with Showalter on this one. Better to go down fighting than to play rope-a-dope with a charging Pillsbury.
Showalter's 23...Qh4 was perhaps too much of a good thing, and I have to agree with the Tournament Book that Pillsbury could simply have traded Qiueens with 24. QxQ and after 24...RxQ played for a prosaic win with 25. g4, ultimately winning the exchange. But as Showalter (who knew Pillsbury well from their frequent prior encounters) undoubtedly knew was most probable, Pillsbury looked for a crushing win in the middle game with 24. Qf3.
The crucial moment in the game came after Pillsbury's powerful 25. e6 (following Showalter's weak 24...Nd7). Pillsbury's move certainly looked like a winner, but Showalter kept his head with 25...fxe6 26. fxe6 Nf6. In this position, Pillsbury needed to play 27. e7 immediately. When Pillsbury instead tried the tricky 27. Re4, Showalter pounced with 27...Qh5. Now, Pillsbury had to worry about losing his advanced e-pawn. He tried to keep his attack going with 28. Bc4, but Showalter traded Queens, forcing Pillsbury to play a simplifying combination to avoid losing material. Before long, the game was reduced to a dead-drawn Rook and pawn ending.
While Pillsbury definitely had his chances here, one must admire Showalter's cool head under fire as he weathered the dangerous attack by his famous compatriot.