A seven-goal sizzler in the west saw Galway United look to a more promising future and Shelbourne look to the last eight of the FAI Cup.
A Dayle Rooney brace was sandwiched by goals from Ciarán Kilduff and Ryan Brennan, United equalising firstly through Enda Curran and secondly Mikey Place, the latter having spurned a penalty to put United ahead, before Aaron Dobbs added the fifth for the Reds.
A madcap game like this should have had this place heaving as John Caulfield took over as Galway boss for the first time, the smattering of onlookers treated to a thriller and a hunger for the return of people to watch the football with.
Shels held Shamrock Rovers scoreless in Tallaght recently and have a real chance at cup glory this year, unlike Galway, who have had a shocker of a campaign and now desperately seek to climb into a First Division playoff spot with time running out.
All told, this was FAI Cup combat as it should be: goals, hunger, tough tackles, mistakes, the favourite enduring a scare.
Shels played with the advantage of a strong wind and no home support in the first half. Nine minutes in the first chance. Georgie Poynton, excellent against Shamrock Rovers, swung in a corner with the wind as an ally; Daniel O'Reilly headed wide at the back post, the Shels bench appealing for a penalty.
At the other end, ropey Shels defending allowed Donal Higgins a shot about which Colin McCabe knew little; after Shels failed to clear, Place was involved, having become a father this week and eventually the ball fell for Shane Duggan, who this week became a dad too; he flashed a shot over.
Place played a speculative ball in behind on 21 minutes and Dano Byrne made a hash of it, allowing the returning Curran in. Curran had a free shot on goal but after taking the ball behind McCabe, McCabe brought him down, Caulfield baying for a red card that would indeed have been the case before the rules changed for genuine attempts at a tackle in the box.
Up stepped Place, who blazed over.
Despite that setback, Galway grew in belief. Shane Doherty found Curran, whose shot failed to trouble McCabe, half an hour in.
At the other end, Denzil Fernandes was fouled just outside the box by the returning Killian Brouder, who has been such a loss for United so far this term. And Rooney, with gorgeous precision, evaded the wall and Matt Connor with a precise left-footer. Galway were reeling as the half-time break neared, and were fortunate that Ryan Brennan blasted over.
The wind and a half-time pep-talk from Caulfield saw Galway on the front foot, Doherty forcing McCabe to save, early on. At the other end, Kilduff got ample power, too much indeed, behind his 20-yard effort.
Conor Barry, who has had such a disappointing season, was introduced at the break and linked up with Curran, who shot straight at McCabe.
Seven minutes into the second half, United were level. The ball broke to Curran after a corner and he drilled home from the edge of the box, the cheers from the locals suggesting there were people at this game after all.
There was a proper cup-tie feel about it now, Denzil Fernandes blocked on the counter as he stretched the United defence. Poynton then curled a cross with the outside of his foot, Brennan heading over. Chrissy Horgan brilliantly headed away at the back post as Dayle Rooney waited to score.
A Place mistake invited Shelbourne to go back ahead 26 minutes into the second half. Alex O'Hanlon pounced and played in Kilduff; Matt Connor got a hand to his chip but it was not nearly sufficient.
Place made immediate amends. Duggan found Doherty on the left; the American, who only left United last term due to the death of his father, ran at Shels; eventually the ball spilled to Place, who bundled it home with the aid of a deflection.
Incredibly, Place was taken off moments after, but Caulfield introduced more pace in the shape of Carlton Ubaezuonu. However, United fell asleep with 12 minutes left, Brennan meeting the rebound after Kilduff rattled the bar.
And United looked beyond recall with six minutes left when Rooney turned cleverly and curled beyond Connor with a lovely strike.
A Kevin Farragher mistake was seized on by Aaron Dobbs, mere seconds off the bench, as injury time began, and United's brief Cup run ended.
Galway United: Connor; Horgan, Farragher, Brouder, Parthoens (Ludden 84); Place (Ubaezuonu 75), Duggan, Nugent, Higgins (Barry 46), Doherty; Curran (Faherty 67).
Shelbourne: McCabe; Ponton (Friel 85), D Byrne, O'Reilly, O'Hanlon; Fernandes (Moore 90), Byrne (Quinn 55), Deegan, Brennan (Kabia 85), Rooney; Kilduff (Dobbs 90).
Referee: Damien MacGraith.
Friday's other cup tie saw Athlone Town come from behind to defeat Wexford Youths 5-3 after extra-time at the Athlone Town Stadium.
After 20 minutes, Wexford were 2-0 up, courtesy of a Jack Doherty penalty and superbly hit volley from Conor English. That's the way things stayed until the break, though the hosts did create chances,
Inside the first ten minutes of the second period, Athlone were level, with Ronan Manning and Taner Dongan on target.
Wexford went back in front on 68 minutes when James Carroll headed home Conor Crowley's free-kick.
Athlone, however, kept plugging away and they were rewarded on 80 when Scott Delaney got on the end of a corner to score.
Into extra-time and the midlanders hit the front a minute in when Lee Duffy headed home Manning's free-kick. Duffy was eventually sent off for a second yellow. That did not deter Athlone, with Adam Lennon on hand to score their fifth.