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
Ceci n'est pas un Amos Burn.
Marshall vs Burn, 1900
(D55) Queen's Gambit Declined, 18 moves, 1-0
"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
Opening errors walk the White K into Black's masterful net.
Glucksberg vs Najdorf, 1929
(A85) Dutch, with c4 & Nc3, 22 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
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
Missed chance to refute sac, then missed chance to draw.
A G Murphy vs C Witte, 1957
(B20) Sicilian, 23 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
D Walker vs Almeida, 1965
(C19) French, Winawer, Advance, 11 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
Enabled a disastrous fork with check on move 3
Z Djordjevic vs M Kovacevic, 1984
(A45) Queen's Pawn Game, 3 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
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
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
Taking the Pawn did nothing to stop the fork.
D Sengupta vs Srinath Narayanan, 2018
(A45) Queen's Pawn Game, 10 moves, 0-1
Blundered away the B 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.
I 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