Southampton's second string were brushed at side at ease by the Whites who join the last eight for the first time since the 1995/1996 season.
An improved performance from Neil Warnock's men saw them overcome Nigel Adkins Southampton to progress into the next round of the Capital One Cup.
In an attempt to freshen things up, Warnock decided to shuffle his pack with Luke Varney and Jamie Ashdown coming into the starting line-up along with Aidy White and Michael Brown. The visitors made countless changes to their line-up after playing in the Premier League on Sunday.
The Whites started the game the better side and were opening up the Saints with White and Byram providing width. Despite having the majority of the ball, United didn't create a clear-cut chance until Luke Varney missed from one yard out after some clever work from Diouf.
Rodolph Austin then joined in with missing easy chances when he drifted into the box unmarked before mistiming his header which went high and wide of the goal towards the South Stand.
Despite his early miss Varney continued to press and work hard and he was nearly rewarded when his right-footed curling shot from outside the box narrowly missed the post. With Southampton struggling at the back, Varney had another chance to capitalise but his chipped effort came back off the upright.
In the 34th minute United finally broke the deadlock thanks to a cool head from Tonge. Varney was once again involved and his run to the byline saw the ball fall to Tonge who calmly slotted the ball into the bottom corner.
The second-half produced much of the same for Warnock's men with the entire team working hard to thwart the Southampton counter attacks. Varney and Diouf were a handful up top, Brown didn't give the opposition a sniff and Tom Lees was once again showing his vast improving skills at the back.
Southampton made a double change and were having more of the ball as the clocked ticked by slowly. The determination from the likes of Jason Pearce helped keep the visitors at bay after some important interceptions and blocks on the edge of the area.
It was all over when Diouf tapped home from 5 yards after a barnstorming run from Austin saw his shot deflected into the path of the Senegalese international. There was time for one more goal for the Whites when Luciano Becchio scored with his touch from the penalty spot after Tonge was bundled over.
After a resounding victory, Warnock and the players need to take this momentum into Friday's difficult encounter against Brighton. The Cup is a great distraction and there's nothing sweeter than beating a side higher than you...regardless of the team sheet.
A takeover could be on the horizon (I've said this so many times), and Leeds have shown some improvements after a sticky patch.
The question is can the players rekindle their form for the league?