The win comes just a week after Ko won Australian Amateur title in Melbourne.
"It's pretty amazing," said Ko, who turns 15 on April 24. "I don't really know what to say ... I'm really happy and to be part of history is like a miracle. It's not something you can have by clicking your fingers.
"It was really nerve-wracking," she added. "I had a few deep breaths out there [on the 18th hole]. I was nervous until the last second. [I was] thinking of last year and I looked back and there were so many people watching."
Ko began the day with a four-shot cushion over playing partner Lyndsey Wright, a 32-year-old who picked up five birdies on the front nine.
But rather than crack, Ko - who dropped just two shots all weekend - hit birdies of her own on eight and 16.
In the end it was Wright who came off second best when posting back-to-back bogeys on 16 and 17 which allowed Morgan, who shot six-under to claim second place.
Wright, who finished in a tie for third, said of Ko: "The only thing I could've done is get my putter out and smack her in the legs.
"She just played wonderful golf and did not make a mistake. It's amazing to see her and think she's only 14.
"This is a historic moment for women's golf. It was no different from playing with a seasoned pro on the LPGA. I put a lot of pressure on, and she did not fall apart at all.
"She's going to be an exceptional player if she keeps doing what she's doing."
With Ko being an amateur, Morgan took home the major prize money of $18,750, but the North Shore golfer will be getting a return of sorts - the satisfaction of knowing her coach Guy Wilson has jumped into Lake Rotoiti.
"Anything that enables me to get soaking wet is an opportunity that she really pushes for, much the same as the amateur win last week," Wilson said of their arrangement.
Wilson caddied for Ko in this tournament 12 months ago but this time had to settle for watching the scoring action online while at his father's house by the lake.
"I would much rather be there and be in control of the situation," Wilson said. "I was going to bed last night at 11 o'clock and I thought 'sh*t I should just fly over' because I knew she would have a very good chance of winning but we just couldn't afford it. Hopefully what she has done today will enable us to afford for her team to be there [in the future]."
While Wilson was disappointed at not being by her side, he was always confident Ko could do the business this time.
"I didn't think she would make too many bogeys. She was definitely going to hit fairways and greens. She may not have been confident enough to hole the puts for birdies but she definitely wouldn't make bogeys so it was up to the other players to pick up five shots and if they didn't do that then the victory was Lydia's."
As for Ko's future, Wilson said not too much had changed for the Pinehurst School student.
"It's not like she's won a billion dollars or something else has turned up on her plate. She's still an amateur, she's going to be an amateur for another three or four years."
