<5.Nc3> was a particular favourite of Tarrasch as White in the Closed Ruy Lopez, and it featured seven times in his 1893 match with Chigorin. Schlechter too had played both sides. Tarrasch as White had defeated Schlechter with this opening in Ostende 1907.
<5...Bb4> was an idea of Morphy's which Chigorin used twice in their match (games 5 and 7). In both games White played <6. Nd5>, but Schlechter preferred to castle king-side in each of the three times he had this position in this match. Schlechter plays the opening in a very conservative fashion and obtains no advantage through is own manoeuvres.
<15...d5> seems thematic but <14...exd4> 15. Bxd4 Nxe4 16. Nh5 Ne5 17. Qe2 Nf6 may have been more accurate. As played Tarrasch is left with a weak isolated pawn on <e4> which is not easy to defend as it is within his opponent's pawn chain.
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<18...Be6> is not a complete answer to Schlechter's 20th move, but <18...Bb6> is no better. 19. Re1 Qc7 (or 19... Bxe3+ 20. Rxe3 Bf5 21. Qh5 g6 22. Qxh6) 20. Bxb6 Qxb6+ 21. Qd4 c5 22. Qf2 with a significant advantage to White.
<18...exd4?> is simply ruinous for Black after 18...exf3 19. Qxf3 Be6 20. Bxe6 fxe6 21. Qf7+ Kh8 22. Rad1 Qe7 23. Rd7
<20...Qd3> intending Qb5 should not have led to equality. It is an attempt to generate some complications as after <20...b5> , for instance, Tarrasch has a very poor game, <21. Rad1> Qe7 22. Rd4 Bb6 23. Rxe4 Bxe3+ 24. Rxe3.
<25. Qxb5> does not seem necessary. Schlechter could have usefully retained the services of his Queen, for example, <25. Qc2> Re8 26. Rd4 c5 27. a4 Qc6 28. Rd6, with a strong initiative. Instead, Schlechter plays very carefully and the game is drawn.