Milton Keynes Dons, who trailed after only 17 seconds but fought back to take control of the game, suddenly fell apart in the closing stages.
Goalkeeper David Martin made a great save to deny Delroy Facey with five minutes left but Hull kept up the pressure.
Dons substitute Jason Puncheon then unnecessarily conceded a corner from which Michael Keane fired home from 20 yards.
Three minutes of stoppage time brought more misery for the Dons when Stuart Green scored his second goal of the match from just outside the area.
Green had set the ball rolling in the game's first attack in which Nicky Barmby sent Facey storming into the area. The striker's shot was blocked but it fell straight to Green who rammed the ball home.
The Dons looked punchless in the first half-hour but gradually settled down and suddenly hit Hull with a brilliant equaliser.
Laurent Herve quickly took advantage of a Stuart Elliott mistake to find Malvin Kamara with a probing pass. Kamara centred and top scorer Izale McLeod side-footed home.
Hull enjoyed a good spell around the hour mark when the Dons pretenders showed signs of the panic that was to come. But Facey edged a cross-shot just wide and floated another effort over the bar.
The game turned in the Dons' favour when Andy Dawson brought down McLeod from behind. However, the striker hit a tame penalty that Boaz Myhill saved comfortably. The Dons protested that Dawson should have been sent off but did not get their wish.
However, they looked like winners when Ben Chorley glanced a near post header past Myhill from Gareth Edds's corner.
But it all went wrong as Hull launched a late bid to salvage something from the game. The Dons lost their shape and started to panic with disastrous results.