How was Fundora able to knock out his opponent in the final second?

The boxer could've simply conserved his energy and patience until the final round, when his opponent was already exhausted and had let his guard down. The last seconds of a fight often see the most dramatic moments, because both fighters are giving it everything they've got, taking bigger risks than usual. One well-placed punch at the right moment - and that's a knockout, even if the entire fight had been going against him.

In the final seconds of a fight, the psychological factor often outweighs physical exhaustion. Fundora could simply wait for the moment when his opponent relaxed, thinking he'd already made it through most of the round - and then a punch catches him off guard much more effectively than early in the fight.

Plus, boxers often lose concentration in the final moments because their brain is already starting to count down to the end. His opponent could've figured there was just a little bit left and dropped his guard - and that's when a precise shot lands and decides the whole match. This happens regularly in professional boxing because the final seconds demand maximum attention, not minimum :)

Don't overestimate the role of luck - a final knockout is usually the result of a fighter working throughout the match to find openings in the opponent's defense. Fundora apparently found a vulnerability and waited for the moment when the guy could no longer defend properly against that specific punch. By the end of a fight, even a well-prepared opponent loses the sharpness of their reflexes, and that's when winning combinations slip through those windows.