Nine-man Glentoran produced an heroic display to qualify for the Setanta Cup final as Jason Hill's early goal saw off holders Drogheda at United Park.
Hill's early goal came after a blunder by keeper Jamie Ewings and while Elliott Morris saved from Adam Hughes, Michael Halliday nearly added a second.
Morris denied Graham Gartland and Paul Keegan missed a penalty after Paul Leeman had been harshly sent off.
As Drogheda pressed late on, Hill was then sent off but the Glens held on.
The defeat will be a major blow for the cash-strapped Drogs who were viewing the 150,000 Euro prize for the competition as a potential financial lifeline.
Hill's third-minute goal came when his mishit shot somehow squirmed through Ewings' legs with the keeper appearing to be unsighted by Michael Halliday's presence.
Ewings then partially atoned for his mistake by saving well from David Scullion while Morris at the other end moved smartly to push away Adam Hughes' close-range effort.
Gary Hamilton was producing an imperious display for the Glens with his trickery causing all manner of problems for Drogheda defender Shane Robinson.
Drogheda's Shaun Maher was lucky to avoid a straight red card after an awful challenge on goalscorer Hill.
Halliday then looked certain to score a second Glentoran goal but he didn't get full purchase on his shot and Gartland got back to make a brilliant last-ditch clearance.
Drogheda pressed after half-time and Morris reacted brilliantly to turn a Gartland header away for a corner.
The Drogs should have equalised on 74 minutes when they were presented with a fortunate penalty after Leeman had tangled with Declan O'Brien.
Leeman did appear to lean into O'Brien but the spot-kick award looked a harsh call and the decision to give the defender a straight red card appeared ludicrous.
But Republic of Ireland Under-23 skipper Keegan lashed his penalty against the bar as Glentoran kept their noses in front.
As Drogheda pressed in the closing stages, Hill received his marching orders two minutes from time after getting his second yellow card for a clumsy challenge.
Drogheda produced a late aerial bombardment but the Glens held firm to secure a famous victory which qualifies them for their first Setanta Cup decider.
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