Forced to battle back from going 2-0 down within 15 minutes, they did so with Chris Smalling's header, a Christmas cracker from Wayne Rooney and James Chester's own goal. (Agencies)
It was rough on former United player Chester who had shot Hull in front after four minutes, but a huge festive boost for the champions who despite not playing well showed their old knack of turning around unpromising situations.
Rooney's equaliser was his 150th in the Premier League for United and the England striker said victory, achieved with 10 men after Antonio Valencia's late red card, was a massive result as United attempt to muscle in on the title race.
"We had some bad results at the start of the season but we are showing our quality now, we are fighting hard and hopefully we can surprise some people now," Rooney told Sky Sports.
Victory lifted United into sixth spot, three points off the top four, before the rest of the day's matches on a hectic holiday programme which includes leaders' Liverpool up against third-placed Manchester City.
The United team did not arrive at the KC Stadium until the hour before kickoff and the champions began like they were still on the coach, falling 2-0 down inside 15 minutes.
Chester put Hull in front, reacting faster than any United defender to volley into the roof of the net after Alex Bruce headed Tom Huddlestone's corner back across goal.
Nine minutes later United's defence was again at sixes and sevens as David Meyler's scuffed shot went in off the shin of Jonny Evans, following a goalmouth scramble.
That left United needing to score three goals to win, the total amount of goals Hull had conceded at home in the league prior to kickoff.
Their response was emphatic. Smalling climbed high to head in Rooney's 19th minute free kick and just past the mid-point of the opening half United were level as Rooney dispatched a dipping, swerving right-foot shot past limping Hull keeper Allan MacGregor.
Rooney's milestone strike seemed set to pave the way for the visitors to go on and win the game comfortably but having drawn level they were forced to go toe-to-toe with a tenacious Hull.
The hosts almost went back in front early in the second half when Bruce, son of manager Steve, rattled the crossbar with a header and they pushed United back with some crisp attacks.
However, Chester's day turned full circle after 66 minutes when the scorer of Hull's opener was faced with a tricky Ashley Young cross with Rooney lurking on his shoulder and could only head the ball into his own net.
When Valencia was sent off for picking up a second yellow card, having kicked the ball away in the 90th minute, Hull threw the kitchen sink at United's goal and Chester looked poise to level but saw his shot saved by David de Gea.
Forced to battle back from going 2-0 down within 15 minutes, they did so with Chris Smalling's header, a Christmas cracker from Wayne Rooney and James Chester's own goal.