Leg-spinner Lokuarachchi's final figures of 4-44 were his best in One-day internationals as the Dutch, chasing 314 to win, were dismissed for 258, with Dilhara Fernando also weighing in with three wickets.
Fernando did the damage at the top of the Dutch batting line-up as he removed openers Bas Zuiderent and Darron Reekers, who top-scored for the hosts with 45 from just 39 deliveries on Thursday.
Fernando also bowled debutant Eric Szwarczynski to leave the Netherlands struggling on 103 for three.
Luuk van Troost (40) and Peter Borren (34) offered brave resistance down the order but when Lokuarachchi dismissed them both it was only a matter of time before Sri Lanka extended their recent winning run, and Farveez Maharoof sealed the victory with the last two wickets.
Upul Tharanga had top-scored with 72 as Sri Lanka piled up 313-8.
The Sri Lankans had hit a One-day international world record total of 443-9 as they crushed the Dutch by 195 runs in the first encounter of this two-match series on Tuesday.
And although they couldn't quite match that feat this time, they were still in complete control again.
Sri Lanka recently completed a 5-0 One-day whitewash of England and were heavy favourites to continue their fine form against the Netherlands, one of the leading six Associate countries who are not a full Test playing nation.
The International Cricket Council (ICC) on January 1 decided to award full ODI status to games involving Associate countries.
Sri Lanka, who rested Sanath Jayasuriya, won the toss and opening batsman Tharanga blasted eight boundaries in his 72 from 72 balls to get the tourists off to a flier.
Tillakaratne Dilshan provided able support with 66 from 59 deliveries but, although the majority of his team-mates got themselves in, no-one else managed to reach a half-century.
The Netherlands handed debuts to Pieter Seelaar and Szwarczynski but medium-pacer Reekers was the pick of his side's attack as he claimed three wickets.
Billy Stelling wasn't so fortunate as he conceded 91 runs from his 10 overs.