Dhananjaya de Silva, who was appointed as Sri Lanka's test skipper in January, made a winning start to his captaincy, as spinner Prabath Jayasuriya took eight wickets in a player-of-the-match performance.
Afghanistan were all out for 198 in their first innings after being put in to bat first by the hosts, with only Rahmat Shah (91) having some success against Vishwa Fernando (4-51), Asitha Fernando (3-24) and Jayasuriya (3-67).
Sri Lanka posted 439 in reply, as former captain Dimuth Karunaratne set the tone scoring 77 off 72 balls. Angelo Mathews (141) and Dinesh Chandimal (107) put the hosts firmly in the lead, despite the best efforts of Naveed Zadran (4-83).
Afghanistan started their second innings well with Ibrahim Zadran (114) building hundred-run partnerships with Noor Ali (47) and Shah (54). But the last six batters contributed only eight runs, as Jayasuriya took a five-wicket haul.
Afghanistan's second innings ended at 296, giving Sri Lanka a target of 56, which their openers chased down in 7.2 overs.
The two teams will play a three-match One Day International (ODI) series starting on Friday, followed by three T20 Internationals.
