A certain game with a knight promotion checkmate I once remember (this happened 2-3 years ago) one of my friends showing me a game that was about 20 moves long. It was maybe a little longer, but it definitely ended in the middle game. It ended with a knight underpromotion checkmate, where the promoted knight both attacked the opposing king, and the knight also defended a rook that blocked off most of the king’s escape squares.
I am not 100% sure, but I think the winning player was down a whole lot of material before the knight promotion. I don’t remember whether the winning player was black or white.
I am sorry if this isn’t enough information to answer the question.
Due to prior knowledge, I scoured these three chessgames.com collections that I knew of. I found two games that match.
They do fit the bill of having the promoted knight protecting a rook. However, they're quite longer than 20 moves, are in the endgame, and have different material balances from what you think. It does help that they are recent games, relatively speaking, I'd say. So while they are similar, they may not be what you are looking for.
[Title &quot;Gawain Jones-Danny Raznikov, Isle of Man Masters, Douglas Isle of Man, 10/12/2014&quot;]
[FEN &quot;&quot;]
[startply &quot;136&quot;]

1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Be3 Ng4 7. Bg5 h6 8. Bh4 g5 9. Bg3 Bg7 10. Be2 h5 11. h4 gxh4 12. Bxh4 Nc6 13. Nb3 Be6 14. Qd2 Qb6 15. Nd5 Bxd5 16. exd5 Nce5 17. c3 Ng6 18. Bf3 Rc8 19. Bg5 N6e5 20. Bxg4 hxg4 21. Rxh8+ Bxh8 22. O-O-O Kd7 23. Qc2 Rg8 24. Qf5+ Kd8 25. Be3 Qb5 26. Bd4 Qd7 27. Qh7 Rf8 28. f4 gxf3 29. gxf3 Bf6 30. Qe4 Rh8 31. f4 Qg4 32. Nc5 dxc5 33. Bxe5 Bxe5 34. Qxe5 Rh4 35. Rf1 f6 36. Qe4 Qd7 37. Qg2 Kc7 38. Qf2 Qb5 39. Re1 Rh7 40. Qg3 Kb6 41. b3 Ka7 42. Qf2 Ka8 43. Qc2 Rg7 44. Kb2 Qd7 45. Qe4 Qg4 46. Ka3 Qd7 47. Rh1 Ka7 48. Rh2 Qd6 49. Re2 Rg4 50. Qxe7 Qxe7 51. Rxe7 Rxf4 52. Rc7 Kb6 53. Rc8 Rf3 54. Kb2 Rd3 55. c4 f5 56. Kc2 Rh3 57. b4 cxb4 58. d6 Rh7 59. Kb3 Ka5 60. Rc7 Rh3+ 61. Kc2 Rh2+ 62. Kd3 Kb6 63. c5+ Kb5 64. d7 Rh1 65. Ke2 Rh2+ 66. Ke3 Rh3+ 67. Kd4 Rh1 68. Rxb7+ Kc6 69. d8=N#


[Title &quot;Martyn Kravtsiv-Ding Liren, World Cup, Tbilisi Georgia, 9/8/2018&quot;]
[FEN &quot;&quot;]
[startply &quot;219&quot;]

1. c4 Nf6 2. Nc3 e6 3. d4 Bb4 4. e3 O-O 5. Bd3 d5 6. Nf3 dxc4 7. Bxc4 c5 8. O-O cxd4 9. exd4 b6 10. Qe2 Bb7 11. Rd1 Bxc3 12. bxc3 Qc7 13. Ne5 Nbd7 14. Nxd7 Qxd7 15. Bd2 Ne4 16. f3 Nxd2 17. Qxd2 Rac8 18. Bb3 Bd5 19. Qd3 Qc6 20. Rac1 Bc4 21. Bxc4 Qxc4 22. Rc2 Rfd8 23. Kf2 h5 24. Qxc4 Rxc4 25. Ke2 b5 26. f4 f6 27. Kd3 e5 28. fxe5 fxe5 29. Rb1 a6 30. Rbb2 exd4 31. cxd4 Rdxd4+ 32. Ke3 Re4+ 33. Kf3 Rf4+ 34. Ke3 Kh7 35. g3 Rfe4+ 36. Kf3 Rxc2 37. Rxc2 Ra4 38. h4 Kg6 39. Rc6+ Kf7 40. Rc7+ Kf6 41. Rc6+ Ke5 42. Rc5+ Kf6 43. Rc6+ Kf7 44. Rc7+ Kg6 45. Rc6+ Kh7 46. Rc2 g6 47. Ke3 Kg7 48. Rc7+ Kf6 49. Rc6+ Kf5 50. Rc5+ Ke6 51. Rc6+ Ke5 52. Rxg6 Ra3+ 53. Kd2 Rxa2+ 54. Kc3 Ke4 55. Rg5 Kf3 56. Rxh5 Kxg3 57. Rh8 Ra4 58. h5 Kg4 59. Kb3 Kg5 60. Kb2 Rh4 61. Ra8 Rb4+ 62. Kc3 Rc4+ 63. Kb3 Rc6 64. Rh8 Rh6 65. Rd8 Kxh5 66. Rd5+ Kg4 67. Kb4 Kf4 68. Rd1 Ke3 69. Kc5 Ke2 70. Rd4 Rh1 71. Rd6 Ra1 72. Rh6 Kd3 73. Kb4 Rb1+ 74. Ka5 Ra1+ 75. Kb4 Kd4 76. Rh4+ Ke5 77. Rh5+ Kf6 78. Rh6+ Kg5 79. Rd6 Ra4+ 80. Kb3 Kf5 81. Rh6 Ke5 82. Rg6 Kd5 83. Rf6 Kc5 84. Rh6 Ra1 85. Kb2 Ra4 86. Kb3 Rb4+ 87. Ka3 a5 88. Rh5+ Kd6 89. Rh6+ Ke5 90. Rh5+ Kf6 91. Rh6+ Kg5 92. Ra6 Ra4+ 93. Kb3 Kf5 94. Rh6 Rg4 95. Rb6 a4+ 96. Ka2 Rb4 97. Rh6 Rb3 98. Rh4 Ke5 99. Rg4 Kd5 100. Rh4 Kc5 101. Rh5+ Kb4 102. Rh4+ Ka5 103. Rh5 Rf3 104. Rg5 a3 105. Rg4 b4 106. Rh4 Rf2+ 107. Kb3 Rb2+ 108. Kc4 a2 109. Rh8 Rc2+ 110. Kb3 a1=N#