Rookie Sri Lankan fast bowler Matheesha Pathirana claimed four wickets to help rescue the hosts after their batting collapse and hand Afghanistan a narrow four-run defeat in Saturday's T20 opener.
Sri Lanka were all out for 160 with six balls remaining and Afghan opener Ibrahim Zadran led the reply, batting through the innings with 67 not out.
But his chase was bereft of support with the next top-scorer Karim Janat making 20 at number seven before Pathirana sent him back.
Pathirana, 21, was given man of the match honours for only his second career T20 match after two quick dismissals that left Afghanistan still short by 11 at the end of the penultimate over.
Afghan seamer Fazalhaq Farooqi took three wickets to help bowl out Sri Lanka after their late-innings collapse.
The hosts were well placed at 146-5 heading into the last four overs but lost the last five wickets for just 14 runs from 25 deliveries.
All-rounder captain Wanindu Hasaranga top-scored for Sri Lanka with 67 after promoting himself to number six, temporarily steadying a lacklustre innings in a 72-run partnership with Sadeera Samarawickrama.
He made his second T20 half-century in just 24 deliveries with an elegant boundary through extra cover off Qais Ahmed.
The partnership was broken in the next over when Samarawickrama chanced a single to covers but a direct hit from Ibrahim Zadran found him run out.
Hasaranga followed soon afterwards after a miscalculated drive to long-off, easily caught by Ibrahim Zadran off Naveen-ul-Haq .
Sri Lanka won the solitary Test of the tour and swept their ODI series against Afghanistan 3-0.
Dambulla hosts the remaining two T20 matches of the series on Monday and Wednesday.