Akmal hit three boundaries and as many sixes during an entertaining fourth wicket stand of 81 from just 45 deliveries with Shoaib Malik, who remained unbeaten on a 31-ball 46.
Ahmed Shehzad was the other notable contributor with 46 off 38 balls after Pakistan captain Shahid Afridi won the toss and elected to bat in the day-night match.
Pakistan lost opener Mukhtar Ahmed in the second over, but Shehzad and Mohammad Hafeez revived the innings with a 42-run partnership for the second wicket.
Pakistan plundered 70 runs in the final six overs to set up a challenging total for the hosts.
Debutant left-arm seamer Binura Fernando conceded 17 runs in the 16th over which included two consecutive sixes by Akmal.
Sri Lanka's captain Lasith Malinga was the most expensive bowler, giving away 46 runs in his four overs.
Pakistan are looking to win the two-match series to complete a triple on the current tour, having clinched the Tests 2-1 and the one-dayers 3-2.