Two goals in a deadly three-minute spell during the first half saw Orient to their seventh home win of the season and curtailed Hull City's climb towards the play offs.
O's strike duo Lee Thorpe and Jabo Ibehre scored the all important goals midway through the first half - and it could have been even worse for Peter Taylor's side.
Ibehre crashed an effort against the post just after the break and headed a good chance wide just before the interval.
After the game a delighted Orient manager Paul Brush said: "I thought we played well, the players were really up for it.
"It's the best first half I have seen in six years. We were carrying the ball forward and taking the game to the opposition. We could have had four or five." While Hull boss Taylor conceded: "Orient's front men were too good for us at the start and we made two very poor mistakes for the goals.
"A few honest words were said at half time. If we want to get into the play-offs or achieve promotion we have got to start playing at 3pm." Orient created several early half chances with Ibehre and Thorpe both going close before John Anderson nipped in to clear a Thorpe header off the line.
It might have been a different story had Gary Alexander scored with Hull's first chance when he rounded goalkeeper Scott Barrett, but O's defender Matthew Joseph was on hand to make a superb goal line clearance.
It came as no surprise when Orient took the lead after 24 minutes, Matthew Lockwood sending in a cross from the left for to fire home.
Before Hull could recover they were two down when Stuart Green missed a clearance and Ibehre swivelled in the box and planted the ball in the top corner.
Taylor made a double substitution at half time and changed his side's shape and the visitors produced a much better second half show.
But for all Hull's pressure O's keeper Barrett had just one save to make when he thwarted Stuart Elliott.
While Orient were always threatening on the break as John Martin, Thorpe, Ibehre and substitute Aaron McLean all went close to stretching the advantage.