Jason Day has parted ways with Steve Williams, widely regarded as the world's most successful caddie, citing a disconnect of "old school and new school".
Former world No.1 Day and Williams agreed to end their partnership after the Australian missed the cut at the opening PGA Tour play-offs event, The Northern Trust last week.
Williams, 55, had caddied for Day in six events since June's US Open and Day missed the cut in two of them, including the British Open, 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.
"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."
Having got his start in the 1970s, 55-year-old Williams is a former caddie for Australian greats Peter Thomson and Greg Norman and was on Tiger Woods' bag for 13 of his 15 major victories in his stint from 1999-2011.
The New Zealander also caddied for Adam Scott when he became the first Australian to win the Masters at Augusta National in 2013.
But Day is among golf's new generation who rely on technology and analytical data to monitor performance and the Queenslander appeared not to gel with Williams.
"It was a disconnect of old school and new school," said Day.
"Steve has become a friend and I have a lot of respect for him. I thank Steve for everything he taught me."
Day will temporarily use friend and fellow tour golfer David Lutterus as a caddie for this week's BMW Championship as he attempts to keep his US PGA Tour season alive at the second playoffs event.
Day is 50th on the FedEx Cup standings and will need a hot result at the BMW to climb into the top 30 who advance to the season-ending Tour Championship the following week.
Day has gone through several caddie changes during the past two years, having sacked long-time caddie Col Swatton on the eve of the 2017 BMW Championship.
Day then had childhood mates Luke Reardon and Rika Batibasaga share bag duties from September 2017 to June 2019, winning two US PGA Tour events in that span.
Australian Swatton, who has coached Day since his early teens, is still his golf instructor.