Defeated or overcome by someone by a very narrow margin or at the final, crucial moment, especially in a race, competition, or athletic event. Primarily heard in UK, Australia, Ireland. The favoured runner held the lead for the majority of the race, but he was beaten at the post by a relatively unknown competitor in the final 100 metres. It appears the current MP has been beaten at the post, being narrowly defeated by the youngest person to ever win a seat in parliament.