"I'm absolutely delighted to win the McCormack Medal," the baby-faced 18-year-old Fitzpatrick said in a statement. "For this to come along at the same time as winning the U.S. Amateur Championship is really special.
"I had a fair idea that if I had a good finish I might be able to scrape it but it was great that it went my way. It has been an amazing few weeks for me ever since the (British) Open and I am really happy to have achieved so much."
Ko earned the McCormack Medal for a third successive year after another excellent season in which she competed in four of golf's major championships and several other events on the Ladies Professional Golf Association (LPGA) Tour.
The 16-year-old's best finish in a professional tournament was a tie for third in the Australian Women's Open while she finished joint 17th in the Wegmans LPGA Championship and shared 25th place in the Kraft Nabisco Championship.
"It means a lot," said Ko, who last year at the age of 15 became the youngest winner on the LPGA Tour with a three-shot victory at the Canadian Women's Open. "And to have won the medal three years in a row makes it more special. It's awesome.
"I won the U.S. Amateur last year. I wanted to win that championship so much and to have won it, it was great. Without winning it, I may not have been able to maintain my position."
The Mark H. McCormack Medals are named in honour of Mark McCormack, a pioneer and founder of the sports marketing industry who also created the world ranking system for professional golf. He died in 2003.
His International Management Group is widely known as the world's largest representative of sportsmen and sportswomen.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Simon Evans)
