Phil Mickelson has turned his back on Yonex, whose clubs he has endorsed since 1992, to sign a five-year deal with Titleist.
The 30-year-old left-hander, who finished second to Tiger Woods on this season's US money list, will start using Titleist equipment in competition from January 1, 2001.
Under the terms of the deal, Mickelson will continue to play Titleist balls and wear FootJoy shoes and gloves. Now he will also play Titleist clubs and carry a Titleist golf bag.
It is not yet clear which irons Mickelson will use, but Acushnet chief Wally Uihlein said: "We will work with him to develop golf clubs that will assist him in his quest to become the best player he can be."
Mickelson recently described Titleist's new Pro V1 ball, due to go on sale in Europe next spring, as "the greatest technological advancement I have experienced in my playing career" and says he is looking forward to working on future developments in the club and ball market.
However, changing equipment carries a risk. Payne Stewart and Nick Price struggled when switched to new irons at the peak of their games while Mark Brooks left Hogan after winning the USPGA in 1996 and has not won since.
Despite his commitment to Yonex, Mickelson, who has won 17 US tour titles, started using his old Ping wedges again this year.
Mickelson is also negotiating a deal with a financial services company to wear its logo on his visor, the value for which, combined with his new Titleist contract, could approach $50 million (£35 million) over five years.
