The New Zealander has won the Canadian Open on two occasions and two other professional events as an amateur and now this victory completes her second victory as a professional following her victory in the Swinging Skirts event in Taiwan late last year and soon after turning to the paid ranks.
Lewis and Ko staged a hard fought battle all week with little more than two shots between them at any stage, the lead swapping on numerous occasions.
Even today both players led at various stages by two but Ko appeared to steal a winning break when she birdied the 13th and 14th to lead by two with four to play but a superb 9 iron at the 16th by Lewis reduced the margin to just one.
Ko made a great par save at the 17th then both birdied the final hole for Ko to win by one over Lewis with Jenny Shin one shot further back after she too had threatened to join the party over the closing stages.
For Ko it was her sixth win in a professional event since her first at the NSW Women's Open in 2012 and the US$270,000 she has earned for this victory takes her earnings for the season to US$505,000 and she is now 5th on the 2014 LPGA Money List.
Lewis' US$163,000 she earned for finishing second this week takes her to second on the money list with Michelle Wie, who finished 9th this week, now atop the list with earnings of US$651,000.
Naturally Ko has a massive lead in the race for the Rookie of the Year title.
Karrie Webb was the leading Australian in 30th position.
The LPGA Tour will now play the North Texas LPGA Shootout in Irving near Dallas