The 28-year-old Norwegian prevailed at Quail Hollow in Charlotte on Sunday for his first PGA Tour title, in only his 15th Tour start.
Reitan earned $3.6m and a two-year exemption, becoming only the second player from Norway to win on the PGA Tour after Viktor Hovland.
He surged ahead with birdies on 14 and 15 as Alex Fitzpatrick, the 54-hole leader, faded, while Rickie Fowler's runner-up finish extended his recent run of strong results.
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