The 23-year-old Spieth joined Tiger Woods as the only players in the modern era with 10 victories before the age of 24. Woods had 15 victories before he turned 24.
Spieth led wire-to-wire at TPC River Highlands, holding a one-stroke edge after each of the first three rounds. He closed with an even-par 70 to match Berger -- who birdied three of the final six holes for a 67 -- at 12-under 268.
Berger, the Memphis winner two weeks ago before missing the cut last week at the U.S. Open, just missed a 50-foot putt from off the 18th green left that would have forced a second playoff hole.