The Texan came into the final day on the back of three consecutive nine-under-par rounds, which gave him a seemingly unassailable seven-shot lead.
Although Reed struggled to emulate his feats this week on Sunday at the PGA West resort's Palmer course, a one-under-par 71 was still more than enough for him to claim victory and ensure superb final rounds from both Ryan Palmer and Zach Johnson were in vain.
Reed appeared on course to continue his superb run when he birdied the par-five second.
However, the 23-year-old, who claimed his maiden PGA Tour title at the Wyndham Championship in August last year, went bogey-birdie-bogey from the fifth.
He remained under par for his round with an excellent 88-yard approach shot on the par-four eighth hole to three feet for his third birdie of the day.
However, his lead had been cut to five shots and that came down even further when he collected two bogeys at the 10th and 12 holes - in-between a birdie.
Reed managed to recover and nervelessly holed a 17-foot birdie putt at the 15th to take his lead to three shots before finishing off with a trio of pars which was enough to join Rory McIlroy and Harris English as the only players under 25 with multiple PGA Tour wins.
Palmer and Johnson's charge up the leaderboard came too little too late to affect the result.
Palmer finished runner-up two shots adrift of Reed despite an unblemished nine-under-par final round, which included an eagle at the last.
In-form Johnson, who began the year by winning the Hyundai Tournament of Champions at Kapalua before finishing in a share of eighth at last week's Sony Open, went one better after carding a sensational 62, with birdies at each of his last five holes.
Fellow American Justin Leonard finished alongside Johnson on 25-under-par overall, while 2005 champion Brian Stuard finished fifth for his third consecutive top-six finish.