The 47-year-old, who was sacked by Woods two weeks ago, caddied for Adam Scott as he cruised to victory at the WGC Invitational on Sunday.
Despite being by Woods’s side when he won 13 majors, the New Zealander said that this week was the best he has experienced on a golf course.
"It's the greatest week of my life caddying - and I sincerely mean that,” BBC Sport quotes Williams as saying. "It's the most satisfying win I've ever had, there's no two ways about it.”
While Williams plans to be with Scott during the US PGA Championship, the caddy has admitted he still feels let down by his former employer.
"I was absolutely shocked that I got the boot, to be honest with you,” he added. “I've caddied for the guy for 12 years, I've been incredibly loyal to the guy and I got short-shrifted.”
Meanwhile, Tiger Woods finished joint 37th in his first tournament appearance for three months.