Donegal will play Tyrone in next weeks Ulster Under-21 football final.
Floodlight failure delayed the action at Healy Park, but it was of no help to Monaghan who were beaten 4-9 to 1-5 by Donegal.
Lorcan Connor scored two of Donegal's goals with the other two from Ciaran Thompson and Jack O'Brien.
Tyrone saw off Armagh 2-12 to 2-8 at Kingspan Breffni Park, Lee Brennan and Conor Meyler scored the goals in the first half for the O'Neill County.
So it's a North West Derrby to see who will win this years title.
Donegal are hoping its third time lucky having lost the last to finals to Cavan.
After Donegal's victory last night Manager Maxi Curran gave his assessment of the win......