The visitors rallied in the second half but notched an own goal after failing to deflect Souttar in minute 59.
Late substitutes Ajdin Hrustic and Awer Mabil kept up the pressure but could not capitalise on their attempts before Maclaren made his third in the closing moments.
“(It’s) my proudest moment in a football jersey,” he told Fox Sports after the match, while conceding that his side squandered a few easy opportunities through the match.
“End of the day we scored five… but looking back we could’ve scored more,” he said.
Striker Kim Shin-wook scored four in South Korea’s 8-0 drubbing of Sri Lanka while Japan triumphed 6-0 against Mongolia in Thursday’s other second round group matches.