Reed, 27 and ranked 24th in the world, grabbed four birdies and three bogeys on the way to a 15-under-par total of 273 at Augusta National Golf Club.
He improved on his previous best finish in a major, a tie for second at the PGA Championship last August.
Former champion Jordan Spieth surged up the leaderboard with an 8-under 64 for 275. The only blemish on his card was a bogey at 18 after nine birdies. He was two strokes in front of Spain’s Jon Rahm, who closed with a 69 for 277.
Northern Ireland’s Rory McIlroy started the day in second place, three shots behind Reed. But his bid to complete a career Grand Slam with a first Masters victory evaporated with a final-round 74 that left him tied for fifth on 279. DM
"We live in capitalism. Its power seems inescapable. So did the divine right of kings." ~ Ursula Le Guin