The sides were level at the break after Mark Stafford had levelled up proceedings following Andy Waterworth's opener for the Glens.
However, Glentoran dominated matters in the second half and goals from Jay Magee and Martin Murray as well as an own goal from Leon Carters eased them to the win.
Ballinamallard had started well with Chris Curran in particular impressing down the right hand side and he had a good shout for a penalty when he went down under a challenge only for the referee to wave away the Mallards appeals.
It was Glentoran though who were to draw first blood as Jim O'Hanlon slipped in Andy Waterworth and he coolly slotted past Alvin Rouse.
The Mallards responded well to this though and with 23 minutes on the clock they were back on level terms as Stafford rose unchallenged to head home a free kick.
Indeed, the Mallards had further chances as Curran cross was met by Feeney, whose header was deflected on to the crossbar.
And another Curran delivery from the right found the head of Carters but his effort flew wide as the score remained 1-1 at the break.
Glentoran upped their game though in the second half and with 54 minutes played Jay Magee fired home from a Stephen Carson free kick.
The Glens never looked back after this and substitute Martin Murray converted at the back post to make it 3-1 before a Ward cross from the right was turned into his own goal by Carters as the game finished 4-1 in favour of Glentoran.