Former World No.1 Day and Williams agreed to end their partnership after the Australian missed the cut at the opening PGA Tour Playoffs event, The Northern Trust.

Williams had caddied for Day in six events since June's US Open and Day missed the cut in two of them, including the Open Championship, while he secured just one top-10 result.

"Parting with Steve was a mutual decision and not an easy one to make," Day told AAP on Sunday.

"It was a disconnect of old school and new school. Steve has become a friend and I have a lot of respect for him. I thank Steve for everything he taught me." – Jason Day

"He is the ultimate pro; it was a real learning experience being exposed to a caddie who has achieved what Steve has. He has worked with the best.

"But it was a disconnect of old school and new school. Steve has become a friend and I have a lot of respect for him. I thank Steve for everything he taught me."

A former caddie for Greg Norman, New Zealander Williams was on the bag for 13 of Tiger Woods' 15 major victories and also carried the clubs for Adam Scott when he became the first Australian to win the Masters at Augusta National in 2013.

- Evin Priest, Australian Associated Press