A delicious double from James Costello helped Dungannon Swifts smuggle three precious Premier League points from the Oval on Tuesday night.
The former Ballymena United striker tormented Glentoran to set up this shock result – one that almost certainly guarantees the Swifts Premier League survival.
Darren Murphy's team are now nine points ahead of second from bottom Donegal Celtic.
It certainly was a shock to the system for Eddie Patterson's team, who were looking to close in on Linfield, who hold third place in the table.
They got off to flyer with Andy Waterworth grabbing an early opener. But strikes from Costello and Michael McKerr earned the Swifts the lead at the break.
Costello hit the goal of the night midway through the second half and, although David Howland headed in a late second for the Glens – the game was done and dusted by that stage.
The Glens enjoyed a dream start with that Waterworth strike after only six minutes, but it's one that will give Swifts goalkeeper Johnny Curran quite a few nightmares.
He came racing off is line to chase down Jason Hill, but the little defender cheekily swept the ball towards the unguarded goal and Waterworth managed to guide it over the line.
Seconds later Curran made amends for his howler when the managed to hold a 20 yard Jimmy Callacher free kick.
Waterworth should really have punished the Swifts on 13 minutes when his pace left Emmett Friars trailing hopelessly in his wake, but Curran again established himself with a telling block.
But the small pocket of home fans, nestled in the grandstand, were stunned into silence four minutes later when Dungannon scored at their first attempt on goal.
Glentoran old boy Neal Gawley whipped in a low corner, which was flicked home by the unmarked Costello, who somehow escaped his marker.
Now playing with a degree of confidence, the Swifts struck again six minutes before the interval.
McKerr forged his way forward from the back, shrugging off the challenge of Callacher and David Howland before lashing the ball into the far corner – a fabulous strike.
Then in first half injury time another howler from Curran went unpunished. He managed to drop a Kevin Bradley cross at the feet of Waterworth and Clarke, but neither could take advantage.
Glentoran re-appeared for the second half with renewed vigour. Clarke tested Curran with a first time shot from the edge of the box, but the keeper got down brilliantly to save at the base of the post.
Seconds later, Martin Murray's neat back-flick provided an opportunity for Jim O'Hanlon, who somehow swept the ball over the crossbar.
But the Swifts responded through that man Costello, who held his head in frustration after seeing his vicious 30 yard drive skim into the side netting.
The former Ballymena United man struck a sensational third goal on 64 minutes. He was sent hurtling through the middle following a superb McKerr pass and the big striker curled home a beauty beyond Morris.
With the fans streaming to the exits, Howland stooped to head in a Stephen Carson cross four minutes from time – it was too little to late for Glentoran.
Glentoran: Morris, Bradley, Hill (Magee 75), Nixon, Callacher, Howland, McAlorum, R Clarke (McComb 66), Waterworth, O'Hanlon (Carson 59), Murray. Subs: Kane, M Clarke.
Dungannon Swifts: Currran, Grieve, Friars, Brennan, O'Neill, S Lavery (PJ Lavery 79), Montgomery, Fitzpatrick, Gawley, Costello, McKerr. Subs: Magee, PJ Lavery, C Lavery, Douglas, Murphy.
Referee: Colin Burns (Newtownabbey).