Sent to bat first by Afghans who won the toss, Ireland made 210 before they were bundled out in the 48.5 overs.
In reply, Afghanistan made 134 before they were all out in the 35.4 overs.
Mark Adair was the pick of the bowlers for Ireland as he took four wickets. Boyd Rankin followed with three wickets.
Earlier, Aftab Alam and Dawlat Zadran claimed three wickets each for Afghanistan while Rashid Khan took two.
Ireland’s total was majorly contributed by Paul Stirling (71) and captain William Porterfield (53).
For Afghanistan, Asghar Afghan’s 29 was highest individual score. Mohammad Nabi made 27.
The sides will meet for their second and final ODI on Tuesday. After that, Afghanistan will face Pakistan on Friday for their first warm-up match ahead of World Cup.