Watson beat out Jordan Spieth in the final round of the tournament, carding a three-under 69 to finish eight under to claim the title for a second time in three years.
"I told my caddie up the 18th that I couldn't remember the last few holes, I was just hanging on and thinking about making pars," Watson told reporters.
"Somehow I did and walking off 18 was a little bit easier this time. I kind of lucked into the last one, this one is a lot different, it was a lot of dedication to get back here."
The 35-year-old was ranked 12th in the world before the competition.