The 17-year-old New Zealander again has the chance to become the youngest major champion in history when she tees off at the Monroe Golf Club in Pittsford tomorrow morning (NZ time).
If she can win her first major title, she will also become the world No 1, as long as Stacy Lewis does not finish a clear second in the event.
Ko, who has recorded eight top-10 finishes and won two titles on the LPGA Tour in her rookie season, is trying to treat the PGA like any other week on tour.
''Winning would be great, but I'm just going to take it day by day,'' Ko told the LPGA Tour.
''If it goes my way, great, and then I become world No 1, it's even better. But I'm not going to think about it. I'm just going to try and enjoy it and try to think of it as a normal LPGA event.''
Ko's best finish in a major remains her runner-up performance at the 2013 Evian Championship in France, when she was still an amateur.
Her best finish this season, as a professional, in a major championship is a tie for 15th at the US Women's Open.
The former NZ Open champion conceded she had been guilty of getting ahead of herself and pushing too hard.
''To me, I didn't perform that well when I thought, 'Oh my God, it's a major. You need to play,' so I'm going to try to think of it as just another tournament, and hopefully I'll hit some good shots and roll in some good putts.''
Ko will have a good look at her main rival, as she will play her first two rounds alongside Lewis and Swedish major champion Anna Nordqvist in one of the tournament's feature groups.
