Killumney showed their attacking intent from the off with a blistering approach and after Aaron Spriggs needed to be sharp to cut out an intended cross for Manahan, the hosts threatened again with Dennehy crossing for Manahan who knocked it back for Dalian Roche to rifle narrowly over.
Manahan was in the thick of the action minutes later, this time drilling agonisingly over from Dennehy’s low cross.
Killumney were relentless at this point and the inevitable happened on ten minutes when Kevin O’Crualaoi picked out the available Manahan to slot into the bottom corner.
The hosts continued to press with Manahan producing a decent run before skipping past Dijokas to test Spriggs with a stinging low effort.
Glenthorn weathered this early onslaught and started to show signs of composing themselves with Robbie Coade drilling narrowly wide across goal.
Soon afterwards, John Lynch was forced to stretch and tip out for a corner from a decent effort by Dave Dooling.
Then, a chance arrived for Glenthorn to grab the equaliser, but from Liam Coughlan’s corner, Dave Noonan failed to make his free header count.
A crisply struck free kick from Glenthorn’s Niall Martin had John Lynch clasping on to possession at the second time of asking.
Glenthorn were having a good spell now and an inviting cross from the right by Robbie Coade had just too much on it for the in-rushing James Leahy.
But, on the break, Danny Kelly found Luke Dennehy who picked out Manahan in a good position – only to see the ball screw off the strikers foot while in a good position.
After another counter-attack, Manahan was unlucky to see his stooping header flash past the upright from Dennehy’s cross.
Following a lovely move, David McSweeney plays a neat one into space for Manahan who was denied by a tremendous block from Spriggs.
Killumney were in control now again and it was Spriggs who was called upon again to parry from Dennehy before producing another big block sharply when Danny Kelly fired the re-bound straight at him.
But, a second followed for Killumney when a looping delivery from Luke Dennehy dipped over a helpless Aaron Spriggs on 34.
Then, when Dennehy picked out Danny Kelly with a neat pass, he swivelled in the box – only to see Dominic Kelly produce a fine block to save the day.
Further pressure continued from the home side with Kevin O’Crualaoi forcing Spriggs to produce yet another fine block from his firm effort and before the break, Dennehy fed Kelly who turned before rifling agonisingly over.
Killumney extended their lead with just minutes into the second period when a lovely ball from Danny Kelly reached Manahan who showed driving perseverance before forcing home his second and his side’s third.
A hand ball in the box on 57 minutes presented Glenthorn with an opportunity to reduce the arrears and that they did when Robbie Coade slammed home from the spot despite Lynch getting a touch to it.
But, on the hour, Killumney stretched their lead further when Manahan found David McSweeney with a lovely ball down the channel and from the wide area, McSweeney picked out Danny Kelly who sent a first time effort crashing into the Glenthorn net – 4-1 to Killumney on 60 minutes.
There was no way back for a brave Glenthorn as Killumney managed the game out competently in the end with some well controlled possession football.
Killumney Utd: John Lynch, Evan Hogan, Michael Kelleher, Jack O’Driscoll, Alan O’Flynn, Kevin O’Crualaoi, David McSweeney, Dalian Roche, Luke Dennehy, Jamie Manahan and Danny Kelly.
Subs: Evan White and David O’Callaghan for David McSweeney and Kevin O’Crualaoi (63), Jason McSweeney for Jamie Manahan (70), Sean Hume for Danny Kelly (78), Darren Kelly for Jack O’Driscoll (81).
Glenthorn Celtic B: Aaron Spriggs, Dominic Kelly, Ramunas Dijokas, Tomas McGrath, Jordan Lambrid, James Leahy, Dave Dooling, Robbie Coade, Liam Coughlan, Niall Martin and Dave Noonan.
Subs: Anthony Kiniry and Danny Skillington for Dominic Kelly and Dave Noonan (50), Josh Barry for Anthony Kiniry (55), Josh Glavin for James Leahy (63),
Referee: Mick O’Flaherty