Bath suffered their first defeat in an English cup final as underdogs Leeds survived the loss of two England backs to injury to win the Powergen Cup.
Iain Balshaw and Phil Christophers both departed within 25 minutes but tries from Chris Bell and Andre Snyman helped the Tykes to a 20-9 half-time lead.
Gordon Ross added two penalties, while Bath fly-half Chris Malone kicked four.
Despite Bath dominating territory and possession in the second half, Leeds held on for their first major trophy.
The Tykes defended brilliantly as the match wore on and Bath's error count mounted as the clock ticked down.
Bath now have to pick themselves up to try to qualify for the Premiership play-offs, while Leeds will be in next year's Heineken Cup if they preserve their top-flight status.
Leeds suffered a major setback when in-form captain Balshaw, named in the Lions squad earlier in the week, was forced off with a leg injury after just three minutes.
But they did not let that early setback affect them despite Malone putting Bath ahead with the first of three first-half penalties.
Man-of-the-match Ross punished Bath indiscretions at the breakdown with two long-range efforts from just inside the Bath half in the 12th and 18th minutes.
The Tykes lost a second England international after 25 minutes when Christophers was forced off after a kick to his ribs from his own scrum-half, Alan Dickens, at a ruck.
But after an excellent break-out when they should have scored, only for prop Mike Shelley to ignore the numbers out to his left, Leeds grabbed the first try on the half-hour.
The impressive Ross glided through a gaping hole in the Bath midfield and chipped over the remaining cover where Bell claimed the ball and forced his way over.
Ross converted for a 13-3 lead, but two more Malone penalties hauled Bath to within striking distance as the interval beckoned.
But the Australian fly-half then suffered a horror moment when his speculative long pass was intercepted by Snyman on his own 22.
The former Springbok promptly beat the only man in front of him and strolled 70m to the line, Ross converting for a 20-9 half-time lead.
Bath couldn't find a way through
When Malone landed his fourth penalty five minutes after the resumption, the stage appeared set for a Bath fightback.
But another effort hit an upright after 50 minutes and despite plenty of possession generated by their pack, Bath's backs looked clueless as to how to turn it into points.
A botched overlap with 17 minutes left was typical of their lack of craft, and when Malone pushed a penalty wide with 10 minutes left, Leeds sensed it would be their day.
Despite not scoring a point in the second half, they held on with some desperate defence.
Number eight Alix Popham brilliantly stole possession close to his own line and Snyman knocked back Matt Perry with an all-enveloping tackle.
Referee Dave Pearson's final whistle sparked wild celebrations in the Tykes' ranks, and utter despair in Bath's.
Bath: Perry, Maddock, Higgins, Barkley, Welsh; Malone, Walshe; Stevens, Mears, Bell, Fidler, Grewcock, Lewis, Scaysbrook, Feaunati.
Replacements: Humphreys, Flatman, Delve, Hudson, Daniel, Wood, Davis.
Leeds: Balshaw (capt); Snyman, Christophers, Bell, Biggs; Ross, Dickens; Shelley, Regan, Kerr; Hooper, Palmer; Morgan, Parks, Popham.
Replacements: Holt, Rawlinson, Dunbar, Hyde, McMillan, McMullen, Albanese.