After leading by one overnight, it was a tense final day for the man from Gloucestershire as he started in poor fashion.
Casey dropped three shots early on, allowing the chasing pack to apply pressure right up to the 18th hole.
The Englishman was level with Jason Kokrak at eight under on the 18th, but following a bogey from the American, Casey took his chance to finish with a par.
“It was messy but this course was so difficult and I did make errors. Looking at 72 holes, it was hard work.” said Casey after his first win since last year’s victory.“
After being one shot in front of Dustin Johnson going into the final round, Casey expected a battle for the championship with the American.
However, pressure came from South African – Louis Oosthuizen who made sure that if Casey didn’t finish with a par on the 18th, a three-way play-off would decide the tournament victor.
41-year-old Casey added: “In my mind, it was like I was against the world number one – so beat him and I’ve got it. It turned out to be a very different scenario and I feel so good right now.”
The win now leaves him as 13th favourite to win the masters, ahead of the likes of Bubba Watson and last years winner, Francesco Molinari.