Why are world-class engines playing like this? I was reading about the Lc0 engine and its evolution. Then took a glimpse at the games between Lc0 and the notorious Stockfish. I am not a professional or anything remotely close, but this particular game seems very odd to me. According to chess.com:


  The Lc0 engine got off to a fast start in the bonus games, beating the reigning Computer Chess Champion Stockfish despite Lc0 starting down a pawn in the odds-chess position. In typical Leela style, the engine underpromoted to a rook to drive the win home.


[FEN "CCCC 1: Rapid Rumble (15|5) Bonus Games"]
[Date "2018.10.03"]
[White "Lc0 17.11089"]
[Black "Stockfish 220818"]
[Time "09:33:10"]
[TimeControl "900+5"]

1. f4 Nh6 2. f5 Nxf5 3. Nf3 Nh6 4. Ng1 Ng8 5. e4 e6 6. Nc3 d5 7. d4 Bb4 8. e5
Qh4+ 9. g3 Qd8 10. a3 Bf8 11. Be3 Ne7 12. Nf3 Nf5 13. Bg5 Be7 14. Bxe7 Nxe7 15.
Bd3 h6 16. b4 b6 17. O-O O-O 18. Ne2 c6 19. a4 c5 20. c3 Nbc6 21. Qd2 Bd7 22.
Rae1 Rc8 23. b5 Na5 24. Nf4 cxd4 25. cxd4 Qc7 26. Rc1 Qd8 27. Rxc8 Qxc8 28. Nh5
Nc4 29. Qf4 Ng6 30. Nf6+ Kh8 31. Qc1 Na5 32. Qd2 Nc4 33. Qc1 Na5 34. Bxg6 Qxc1
35. Rxc1 gxf6 36. Bh5 Nc4 37. exf6 Kg8 38. Ne5 Nxe5 39. dxe5 Rc8 40. Rxc8+ Bxc8
41. Be2 d4 42. Bf3 h5 43. Bxh5 Bb7 44. Kf2 Be4 45. Ke1 d3 46. Kd2 Kf8 47. Ke3
Bh7 48. Bd1 Ke8 49. g4 Kd8 50. Kd2 Ke8 51. Ke3 Kf8 52. Kf3 Ke8 53. Kf2 Kd7 54.
Ke3 Kc7 55. h4 Kc8 56. h5 Kd7 57. Kf3 Ke8 58. Kf2 Kf8 59. Ke3 Kg8 60. Kf4 Kh8
61. Kf3 Bg8 62. Ke4 Bh7+ 63. Kf4 Kg8 64. Ke3 Kf8 65. Kf2 Be4 66. Ke3 Bh7 67. Bb3
Kg8 68. Bc4 d2 69. Kxd2 Be4 70. Be2 Bb7 71. g5 Be4 72. Bd1 Kh8 73. Kc3 Kg8 74.
Be2 Bf5 75. Kd2 Bb1 76. Bd1 Kf8 77. Kc3 Ke8 78. Kb2 Bh7 79. Kc3 Be4 80. Kd2 Bf5
81. Ke3 Bb1 82. Kf3 Kf8 83. Ke3 Ke8 84. Kd4 Kf8 85. Kc3 Bh7 86. Be2 Kg8 87. Bg4
Be4 88. Bd1 Kh8 89. Kd2 Bh7 90. Bg4 Kg8 91. Bd1 Kf8 92. Bb3 Ke8 93. Bc4 Kd7 94.
Be2 Ke8 95. Kc3 Kf8 96. Bd1 Bb1 97. Bg4 Be4 98. Kd2 Kg8 99. g6 fxg6 100. Bxe6+
Kf8 101. h6 g5 102. Ke3 Bg6 103. Bd5 g4 104. Kf4 g3 105. Kxg3 Ke8 106. e6 Kd8
107. Kf4 a6 108. bxa6 Be8 109. a7 Kc7 110. a8=Q Kd6 111. h7 Kc5 112. h8=R Bd7
113. Ke5 Kb4 114. Rh3 Bxa4 115. Kd4 Bd1 116. Bc6 Bb3 117. f7 b5 118. f8=Q# (118.
f8=B#) 1-0


Ok, I can understand that Lc0 gives a pawn in advance —maybe to show off its superiority, but the rest of the game is full of unbelievably stupid moves. And ironically, those amateur moves are coming from both sides. For example, even for someone like me, 9. g3 Qd8 is hard to believe.

I also can understand that in rapid games, stupid moves are likely to happen. But these are chess engines who can find almost perfect moves in a fraction of second (well, according to my personal experience with Stockfish). So time limit cannot be such a heavy barrier. Then why are they playing dumb like this? Is it intentional or something?
Basically, the first four moves were implemented to start a game without the f2 pawn, i.e., with an imposed handicap. The game starts at move 5 with a French Defense set-up for Black. I'm surprised that Lc0 can win against Stockfish with a pawn down. I would probably have chosen to play e5 than e6, with the idea to install a Bishop in c5 and try to take advantage of the open g1-a7 diagonal.

I was also intrigued by some of the positions and their seemingly dumb moves, but some of them are not that dumb! 

You mentioned a first puzzling moment after 9.g3

Lc0 has a pawn down and Stockfish plays to win with Qd8! By taking in h1 Stockfish could be even worst. Then, we may question the Qd8-h4-d8 sequence that has the advantage of weakening the kingside but loses two tempi. Reacting by c5 instead of Qh4 was probably more natural.

[FEN "rnb1k1nr/ppp2ppp/4p3/3pP3/1b1P3q/2N3P1/PPP4P/R1BQKBNR b KQkq - 0 1"]
[title "Position after 9. g3"]


9... Qd8! {was played and Lc0 has a pawn down and Stockfish plays to win with Qd8!} (9... Qe4? {is the obvious move but} 10.Kf2 Qxh1 (10...Bxc3 11.bxc3 Qxh1 12.h3!! is a transposition) 11.h3!! 11...Bxc3 12.bxc3 Qe4 13.Nf3! {White can maybe play for a win here because I don't see how the Queen escapes!} (13.Bd3 Qh1 14.Bf1=))


The second one is after the massive exchanges 41.Be2

White has winning chances in this endgame and Stockfish tries to find some counterplay by playing 41... d4. Assume Black waits and plays Bb7-Ba8 without playing d4. Then, the winning plan for White is to bring the King to h5 to collect the h6 pawn.

[FEN "2b3k1/p4p2/1p2pP1p/1P1pP2B/P7/6P1/7P/6K1 w - - 0 1"]
[title "Position after 40... Bxc8"]

1.Be2! d4 (1...Bb7 2. Kf2 Ba8 3.Kf3 Bb7 4.Kg4 Ba8 5.Kh5 Kh7 6.Bd3 Kg8 7.Kxh6+-)




Update. There are still some positions where like @polfosol I can't understand Lc0 moves! For instance, after 78... Bh7, the move 79.Kc3 seems indeed quite "dumb"! After 79.Bc2! the win is very easy (at least for a human ;-). 

[FEN "4k3/p4p1b/1p2pP2/1P2P1PP/P7/8/1K6/3B4 b - - 0 1"]
[title "Position after 78... Bh7"]