The leading girls all posted steady scores in round three, but it was Matsumoto who maintained her narrow lead heading into the final round.
With nine holes to play Matsumoto was still a few shots clear before Khoo finished strongly with three birdies on the last four holes. Campbell forced a three-way playoff with a final round of 78.
A four-hole aggregate score playoff on holes 10, 11, 12 and 18 followed.
Matsumoto, Campbell and Khoo all started with bogey on the tight 10th hole.
Campbell and Matsumoto composed themselves to par the 11th while Khoo posted another bogey.
Campbell drained a slick downhill put for birdie on the 12th to extend her advantage, before removing all doubt with a birdie on 18.
In so doing she became only the second international player to win the tournament.
The result came swiftly on the back of a fine result for Smith.
The youngest ever senior champion of Mount Maunganui fired a final round 68 to take out the South Australia Junior Amateur Champs played at the Kooyonga and North Adelaide Golf Clubs by two strokes.