As in horse racing.

[zabado]

Why do we say "pipped at the post"?.

[boxtops]

defeated by the width of a pip

[Zacs-Master]

The Oxford English Dictionary has under "pip v(3)" definition 1c
c. To anticipate or forestall (someone) in a
particular activity, circumstance, etc.; spec. in phr. to pip at (or on) the post, to defeat by a narrow margin at the last moment.

[elzee53]

My brother would say "Won by a drop of snot" :^)

[elzee53]

Sorry I meant: "Beaten by a drop of snot"