CIARAN Martyn handed Glentoran the early advantage with a 16th minute header after connecting with a looping Gary Hamilton corner.
Jim O'Hanlon might have added a second within six minutes from a Stephen Carson cross.
At the other end Stefan Lavery was denied by the feet of Elliott Morris before the visiting keeper came to their rescue again to deny a Johnny Topley snap shot.
Glentoran doubled their advantage four minutes into the second half when, from a Carson left sided cross, Hamilton volleyed into the top corner from eight yards.
Andrew Waterworth made it 3-0 on 66 minutes - only 40 seconds after coming on for O'Hanlon - with a back post finish from yet another Carson delivery.
Another substitute, Darren Boyce, added a fourth in the 85th minute with Carson once more being the provider after turning Dermot McCaffrey to lay the ball off.
Martyn then completed the scoring in the 90th minute after getting on the end of a Carson through ball.
Dungannon Swifts: Morgan, Mullan, McClean, McMinn, McCaffrey, Fitzpatrick, McGerrigan, Topley, Murphy, McCluskey, S. Lavery subs Montgomery, Campbell, Funston, Baldwin, McCready
Glentoran: Morris, Nixon, Martyn, Ward, Howland, Carson, Hamilton, Gibson, Hill, Callacher, O'Hanlon subs Clarke (replaced Howland 81), Taylor (not used), Waterworth (replaced O'Hanlon 65), Boyce (replaced Gibson 83), Hogg (not used)
- Ryan Mullan shadows Jim O'Hanlon (Picture: Russell Pritchard/PressEye.com)