"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, another LPGA event."
Ko's best finish in a major remains her runner-up 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 admitted she has 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.
Meanwhile, New Zealand No 4 Michael Hendry will spearhead an 11-strong Kiwi contingent competing at the US$1 million ($1.19 million) Fiji International this week.
The 34-year-old Japan Tour pro will be joined by Josh Geary, Nick Gillespie, Mark Brown, Ryan Fox, David Smail, David Klein, Gareth Paddison, Richard Lee, Michael Long and Mahal Pearce at the tournament that is co-sanctioned by the PGA Tour of Australasia and OneAsia Tour.
The Fiji International will be played at Natadola Bay Championship Golf Course from tomorrow to Sunday and will be Fiji's first globally broadcast golf tournament.
The Kiwis will play alongside two of the greats of the game in former World No 1 Vijay Singh and South African legend Nick Price.
Both Singh, who is the designer of Natadola, and Price are three-time major champions.
North Shore golfer James Beale has missed the cut at the US Amateur in Georgia.