9. Ng5 weakened things, and there are doubts r.e. the followup.
E D'Andre vs De Vere, 1867
(A02) Bird's Opening, 14 moves, 0-1
Unguarding the back rank
J S Stanley vs C G Heydon, 1872
(C42) Petrov Defense, 28 moves, 0-1
40. ... Re1?
Bird vs W Pollock, 1889
(B01) Scandinavian, 56 moves, 1-0
Bishop exchange -- very bad idea
M Porges vs Winawer, 1892
(B06) Robatsch, 22 moves, 0-1
Resigned immediately after 44.c4??
Lasker vs F R Gittins, 1897
(C45) Scotch Game, 44 moves, 0-1
Ceci n'est pas un Amos Burn.
Marshall vs Burn, 1900
(D55) Queen's Gambit Declined, 18 moves, 1-0
With the K-side weakened, the Pawn hunt loses to a King hunt.
L Karpinski vs Marshall, 1901
(C43) Petrov, Modern Attack, 27 moves, 0-1
"Take my wife--Please!"
K B Finn vs W C Palmer, 1903
(D08) Queen's Gambit Declined, Albin Counter Gambit, 10 moves, 0-1
When setting up a mate net, still mind your opponent's threats!
Duras vs A E Post, 1904
(C77) Ruy Lopez, 23 moves, 1-0
Queened the Pawn--and then threw it away.
Dus Chotimirsky vs Alapin, 1908
(D02) Queen's Pawn Game, 78 moves, 1-0
Hanging a piece as recapturing leads to back-rank mate
Tarrasch vs Lasker, 1908
(C49) Four Knights, 26 moves, 0-1
Too greedy in the opening
J Krejcik vs Baumgartner, 1914
(C40) King's Knight Opening, 7 moves, 1-0
Blundered away the Knight
J Mieses vs Euwe, 1921
(C45) Scotch Game, 12 moves, 1-0
Poaching crows--a terrible mistake
H Walkerling vs Hanssen, 1928
(B40) Sicilian, 10 moves, 1-0
Opening errors walk the White K into Black's masterful net.
Glucksberg vs Najdorf, 1929
(A85) Dutch, with c4 & Nc3, 22 moves, 0-1
5.Nc3 did nothing to parry My Little Checkmate.
M Warren vs Jan Selman, 1930
(B20) Sicilian, 5 moves, 0-1
Watch out for peer pressure!
A Ebralidze vs Ragozin, 1937
(E60) King's Indian Defense, 45 moves, 0-1
The P isn't truly pinned if capturing the R is a blunder.
V G Kirillov vs Blankstein, 1938
(C04) French, Tarrasch, Guimard Main line, 10 moves, 0-1
exd3?? == falling for one fast-acting poisoned Pawn.
H Haberditz vs Hysek, 1938
(A04) Reti Opening, 8 moves, 1-0
Black's QBP was a golden dart frog for White's Q!
W Adams vs G Kramer, 1946
(B12) Caro-Kann Defense, 9 moves, 0-1
Petrosian has Bronstein skunked--and blunders away his Q
Petrosian vs Bronstein, 1956
(E66) King's Indian, Fianchetto, Yugoslav Panno, 36 moves, 0-1
Missed chance to refute sac, then missed chance to draw.
A G Murphy vs C Witte, 1957
(B20) Sicilian, 23 moves, 0-1
19. Kh1 didn't work, then a later Queen trade lost fast.
M Tamburini vs E Paoli, 1957
(A44) Old Benoni Defense, 30 moves, 0-1
Opening enemy lines for a mate in two
Sliwa vs B Malich, 1957
(A43) Old Benoni, 45 moves, 0-1
Naturally, the first Chess computer was a total patzer.
Bronstein vs M20, 1963
(C34) King's Gambit Accepted, 23 moves, 1-0
Knight-snatching enables checkmate net.
A Matanovic vs J H Donner, 1965
(C70) Ruy Lopez, 21 moves, 0-1
D Walker vs Almeida, 1965
(C19) French, Winawer, Advance, 11 moves, 1-0
No time to prepare a fianchetto!
P Pantelidakis vs F Rhine, 1974
(A02) Bird's Opening, 6 moves, 0-1
Wrong stable for that horse!
A Seppelt vs Leganki, 1950
(C07) French, Tarrasch, 6 moves, 0-1
Pawn-snatching into a two-pin combination.
Robatsch vs Jansa, 1974
(A10) English, 14 moves, 1-0
Forty minutes of thought for THAT sort of blunder!?
Gligoric vs Ulf Andersson, 1974
(E44) Nimzo-Indian, Fischer Variation, 5.Ne2, 49 moves, 1-0
4. d4 parried mate aspect but not the rest of the threat.
A Riemslag vs P Cameron, 1978
(A02) Bird's Opening, 9 moves, 0-1
In the opening, watch out for threats to King Bishop 2!
J Henningsen vs R Borik, 1979
(A00) Uncommon Opening, 7 moves, 1-0
Enabled a disastrous fork with check on move 3
Z Djordjevic vs M Kovacevic, 1984
(A45) Queen's Pawn Game, 3 moves, 0-1
A fork of King and Rook that did nada to address White's attack
G Minchev vs B Ganchev, 1986
(B02) Alekhine's Defense, 13 moves, 1-0
11. Na3 did nothing to stop the checkmate.
B Wall vs S Millimaci, 1988
(B22) Sicilian, Alapin, 11 moves, 0-1
Yes the Queen was left en prise/Yes Black right away did seize
R Suess vs O Zenker, 1989
(A80) Dutch, 7 moves, 0-1
This was an easily-won K+P+P vs. K endgame, right?
Dreev vs R Wessman, 1990
(D45) Queen's Gambit Declined Semi-Slav, 77 moves, 1/2-1/2
What sort of opening play is THAT!?
M Mas vs R Guerrero, 1991
(C00) French Defense, 12 moves, 1-0
That horse left Her Majesty badly overworked.
R Gonzalez vs Tal, 1992
(B32) Sicilian, 26 moves, 0-1
Uh, that Bishop was guarding the mate square.
Karpov vs Bareev, 1994
(C07) French, Tarrasch, 36 moves, 1-0
For Pete's sake, don't castle onto a pawnless side!
Ivanchuk vs Topalov, 1996
(B81) Sicilian, Scheveningen, Keres Attack, 23 moves, 0-1
Leaving the Rook en prise
Piket vs Anand, 1998
(D86) Grunfeld, Exchange, 60 moves, 1-0
Hangs a Bishop for a Pawn
Nisipeanu vs Ivanchuk, 1999
(C45) Scotch Game, 14 moves, 1-0
Leading with the Lady against a former World Champion?
Boris Becker vs Kasparov, 2000
(C20) King's Pawn Game, 18 moves, 0-1
Castling into it
U Capo Vidal vs E Gonzalez Chavez, 2001
(A54) Old Indian, Ukrainian Variation, 4.Nf3, 19 moves, 1-0
Bacrot vs M Vukic, 2004
(A46) Queen's Pawn Game, 29 moves, 1-0
Developing the Queen directly into the line of fire
A Gautam vs J Worell, 2004
(C65) Ruy Lopez, Berlin Defense, 8 moves, 1-0
16. ... Ne3?? turns White's opening blunder into a sac.
A Smirnov vs V Shepelev, 2005
(A00) Uncommon Opening, 22 moves, 1-0
Carlsen vs Bareev, 2005
(B12) Caro-Kann Defense, 46 moves, 0-1
Critical failures on both their spot checks.
Wen Yang vs Z Almasi, 2007
(A20) English, 39 moves, 0-1
A N move in self-offense--B cannot now capture K-&-R-forking N.
Shirov vs Kramnik, 2010
(E20) Nimzo-Indian, 38 moves, 1-0
4. Bg5?? and Black gets to kick White's K around.
M Murara vs I Scott, 2012
(A51) Budapest Gambit, 13 moves, 0-1
131.Rc4?? 131.Ka2 with the perpetual would have been better.
A Giri vs Karjakin, 2014
(A35) English, Symmetrical, 131 moves, 0-1
Taking the Pawn did nothing to stop the fork.
Sengupta vs Srinath Narayanan, 2018
(A45) Queen's Pawn Game, 10 moves, 0-1
Blundered away a vital Bishop in the opening.
Ameyalli Avila Fraire vs S Logothetis, 2019
(A07) King's Indian Attack, 11 moves, 1-0
Dodged the 77. a6? trap, but blundered a different way.
Nepomniachtchi vs Anand, 2019
(A21) English, 77 moves, 0-1
150. ... Kc1 loses just four moves away from a 50-move draw
V Kovalev vs D Gavrilescu, 2019
(C07) French, Tarrasch, 152 moves, 1-0
A fatal misclick about to cost the Queen
Nepomniachtchi vs Carlsen, 2020
(C60) Ruy Lopez, 38 moves, 1-0
Marshall's 1940 P-pushing opening against Ragosin this wasn't.
NN vs F Rhine, 2020
(A40) Queen's Pawn Game, 13 moves, 0-1
White missed 61.Ka4! winning.
A Giri vs A Firouzja, 2021
(C11) French, 67 moves, 1/2-1/2