Armagh set up a quarter-final First Trust Senior Cup tie against Dungannon with this deserved win at Eaton Park.
Last year’s beaten finalists, Ballymena, were never allowed to get up a head of steam throughout the first round game.
Armagh dominated the first half for 37 minutes, but only had a converted try and penalty to show for their efforts.
Stephen Morton crossed for the opener - it was just reward after some forward domination from the visitors - after 11 minutes. Winger Ryan Purvis converted for the 7-0 lead.
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The constant rain did not make for good open rugby, but both teams to their credit tried to move the ball.
Armagh continued to dominate proceedings but the home defence were well organised and Purvis, who missed a penalty on eight minutes, slotted over seven minutes from the interval.
Having made some wholesale changed to the front row, Ballymena had come into the game a bit more and in what was their first attack into the Armagh 22, the pack drove over from a lineout and replacement Chris Allen came up with the ball. Glen Bailey added the extras to make it 7-10.
That momentum swing at the end of the half left one feeling Ballymena would press on at the start of the second half.
However, Armagh started strongly again and two minutes in Purvis slotted over a penalty put six points between the teams.
Ballymena were certainly better in the second half, but errors at key times, wrong options and wayward passes allowed Armagh to hold out.
With the game into stoppage time and Ballymena on the attack, they could snatched a try which could have put them into a winning position.
However, Armagh defended well and two successive rare penalty decisions in their favour saw them pressing the home line.