Oh, who qualified in second position in the stroke-play phase of the event yesterday, quickly took control of her match and by the turn was a massive 6 up.
Another win at the 11th saw her 7 up and although Harford staged a minor fight-back it was a case of too little too late and Oh ran out an easy winner.
Oh will face the 34th qualifier, Pennsylvania's Liz Breed, in tomorrow second round of match-play.
New Zealander Liv Cheng was the only other Australasian to qualify for match play and she would also win her first round match. Cheng who studies at Pepperdine University is originally from Taiwan but moved to New Zealand at the age of 4.