Late lapses in concentration cost St Patrick's Athletic dearly against Bray Wanderers and Dundalk, but there was no catching Liam Buckley's side this time round.
In their previous two top-flight fixtures the Saints leaked crucial goals in the closing stages, but they were well primed for battle at Gortakeegan.
The opening period was a familar sight for Saints supporters this year as the travelling contingent watched their team boss the game, but fail to make the most of their dominance.
There was so much to admire in the crisp manner Pat's passed the ball, but Darren Meenan, Greg Bolger, and Christy Fagan all missed opportunities before the first goal eventually arrived in the 35th minute.
John Russell's right-wing delivery dripped with class and Fagan took maximum advantage of slack Monaghan defending to poke the visitors ahead approaching the break.
Monaghan stayed in touch until the closing stages, when substitute Jake Kelly bagged a brace with sizzling strikes on 83 and 87 minutes before Bolger decorated the triumph in the last minute.
Monaghan UTD -- Bennion; Whelan, McMahon, Byrne, Reynor; R Collins (Ryan, 66), McDonagh, Quinn, Marks; Griffiths (Murphy, 71), Humphrey (Isichei, 54).
St Pat's Ath -- Clarke; O'Brien, Kenna, Browne, Bermingham; Bolger, Carroll, Russell; O'Connor (J Kelly, 61), Fagan (D Kelly, 78), Meenan.
REF -- N Doyle (Dublin).