George Dockrell hit the successful run with two balls to spare after Eire had been set a revised goal of 56 in seven overs, with a seven-wicket victory giving the hosts the five-match contest 3-2.
Eire paceman Mark Adair eliminated openers Hazratullah Zazai and Rahmanullah Gurbaz in his first over after residence skipper Andy Balbirnie gained the toss.
And when Adair dismissed Ibrahim Zadran, he had figures of 3-16, with Afghanistan 26-3 inside 4 overs.
Usman Ghani, nevertheless, led an Afghanistan counter-attack after Josh Little had Najibullah Zadran and captain Mohammad Nabi caught behind by Lorcan Tucker off successive deliveries.
However having made an unbeaten 44, off simply 40 balls — together with three fours and two sixes — Ghani´s innings was curtailed by rain, with Afghanistan 95-5 off 15 overs.
A prolonged delay left Eire chasing a revised goal.
Off-spinner Mujeeb Ur Rahman had Balbirnie lbw for 9 and when he had Paul Stirling (16) caught at midwicket, Eire have been 38-2.
That turned 45-3 when Tucker fell to leg-spinner Rashid Khan for 14.
However Harry Tector and Dockrell then held their nerve as Eire gained with three wickets down.