League Two outfit Bury, with former United midfielder Peter Sweeney in their ranks, had failed to win any of their first three friendlies but fully deserved this victory.
Alan Knill's men looked dangerous in the final third all evening and goals from Ryan Lowe, Andy Bishop (2) and Danny Carlton sealed the Shakers' first victory of pre-season.
Lowe fired home in the first half after being picked out in the penalty area by David Worrall.
Substitute Bishop scored his second goal in as many matches when he clinically slotted past Kasper Schmeichel after a cute ball from strike partner Danny Carlton.
The scoreline could have been worse for the travelling Leeds fans but Worrall's 68th minute effort was ruled out for offside.
Simon Grayson's men piled men forward in the latter stages and came close to pulling one back but Cameron Belford made a stunning save from a Tom Lees header.
Bury made it three with six minutes remaining when Carlton had the simple task of tapping home Danny Hudson's inch-perfect cross from just six yards out.
And the rout was complete in the 88th minute when Bishop converted from the spot after Max Harrop had been felled in the penalty area by Paul Connolly.
Bury: Belford, Picken (Bennett 58), Futcher (Harrop 73), Sodje, Skarz (A Jones 73), Worrall (Nolan 81), Sweeney (Carlton 58), Schumacher (Hudson 81), M Jones (Mozika 58), Haworth (Bishop 58), Lowe (Samuels 58).
Subs (not used): Branagan
Leeds United: Schmeichel, Hughes (Connolly 59), Bromby (Lees 68), Collins, Bessone (White 68), Snodgrass, Kilkenny, Howson, Johnson, Becchio (Gradel 59), Grella (Somma 68).
Subs (not used): Higgs
Referee: Andy Penn (West Midlands)
Attendance: 2,769
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