McDowell was two down after four holes, but then mounted a comeback. He pulled even on the 12th hole, then used a par on the 14th to grab his first lead at Thracian Cliffs Golf & Beach Resort.
McDowell secured the victory on No. 17 when Jaidee couldn't convert a long birdie putt try.
The Northern Irishman, ranked eighth in the world, tapped in for a par, wrapping up his eighth European Tour victory.