The 17-year-old, world No 1, overcame a slight wobble midway through her final round before posting a one-under-par 71 to secure her second national open title in three years.
Three strokes clear after 36 holes ??? thanks to her stunning 61 on Saturday ??? the young Kiwi extended her lead to five shots after making three birdies in her opening six holes on Sunday.
However, a double-bogey six at the eighth, followed by a bogey at the short ninth, threatened to derail her march to the title.
But Ko recovered her composure with birdies and 10 and 12, and she crossed the finishing line four strokes clear of Australian amateur Hannah Green who shot a joint best-of-day 68 to claim second spot.
The win means Ko retains top spot in the ranking thanks to back-to-back successes Down Under ??? she also triumphed at the LPGA???s Australian Open in Melbourne last week.
A delighted champion says she is happy with her early season form: ???I tied second in my first week, tied seventh the week after that, then won my last two events.
“So this is even better than I would ever have imagined. It???s just great to have won the two Opens back to back.???
However, Sunday???s final round was not a good experience for another teenager, Charley Hull, who had teed-off in second spot.
The 18-year-old from England, who was Ko???s playing partner for the third and final round, slumped to a miserable 75 after playing her final seven holes in five-over-par.
Hull, whose opening 43 holes had yielded just a single bogey, finished in a tie-for-sixth, some seven shots behind champion Ko.