Afghan Voice Agency (AVA)_Monitoring, Nissanka did not waste time when the chase began, racing to his seventh ODI half-century in 32 balls with eight fours and two sixes, AFP reported.
He left on 51 after being trapped leg before wicket by Gulbadin Naib to end an 84-run stand for the opening wicket.
Fellow opener Karunaratne, featuring in his first ODI series in more than two years, made 56 not out to ensure that Sri Lanka reached the target without another wicket falling.
His 56 came off 45 balls with seven boundaries, making his eighth half-ton in the format.
Fast-bowling spearhead Chameera established Sri Lanka’s dominance early with two fiery spells at the crease that left the tourists unable to post a decent partnership.
Chameera, playing his first series after ankle surgery that sidelined him for seven months, earned man of the match honors with his 4-63.
Leg-spinner Wanindu Hasaranga polished off the Afghan tail with 3-7 while quick Lahiru Kumara claimed two wickets, leaving the tourists flailing on 116.
Kusal Mendis was unbeaten on 11 as Sri Lanka reached the target in just 16 overs to end the game early.
Afghanistan won the first game comprehensively by six wickets, but Sri Lanka bounced back to take the second game by 132 runs.
Sri Lanka will head to Zimbabwe for World Cup qualifiers in a bid to secure one of the two remaining slots for the format’s showpiece event.
Afghanistan are already through to the World Cup, to be held in India from October.