Sign Of Tiredness

POSITIONAL understanding does not disappear with tiredness, but tactical skills take a big knock.
This is a major reason why chess strength tends to deteriorate in old age - seniors tire more quickly and so make more tactical mistakes.

White to play and lose in Spanton (170) - Robert A Dean (150), Doncaster U171 Round 2

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12.Qd4??
My original intent had been 12.Bb4, which may be enough for a small edge (Stockfish10 reckons so, but Komodo10 rates the position as level). Then I thought: "Why not drive Black's knight back to f6 and follow up with  ...Bb4?"
The answer to my question is …
12...Nxd6 (0-1, 20 moves).