For Sri Lanka, left-arm spinner Viran Chamuditha finished with impressive figures of 2/20 off his 10 overs.
Defending a modest total, Afghanistan found success in the first over with Abdul Aziz snapping the wicket of Chamuditha. Sri Lanka bounced back from the early wicket through Dimantha Mahavithana (37) and Senuja Wekunagoda (43). However, the Afghans gave them a tough contest.
It was all-rounder Chamika Heenatigala (22 not out), who navigated the team through a nervy final phase, taking them home in 46.5 overs.
The result means Sri Lanka, Afghanistan and West Indies all have four points each in the Super Six. Afghanistan still sit atop Group 1 owing to a superior net run-rate.