Reed had fired three straight 63s, setting a PGA Tour record for the lowest-ever 54-hole total in relation to par, and came into Sunday's final round with a seven-shot lead.
His final-round pace wasn't nearly as sparkling, but the 23-year-old Texan had a built a big enough to lead to fend off the field and claim his second career win, ending at 28-under 260 on the Arnold Palmer Private Course at PGA West.
Second place went to Ryan Palmer, who carded a 63 to finish at 26-under 262.
Sole possession of fifth one shot further back went to Brian Stuard (65).
Bill Haas (67) and Brendon Todd (69) shared sixth at minus-23.