Stefani, seeking his first PGA Tour win, finished at 12-under-par 198, one better than second-round leader Harris English.
English fell off the pace with a round of 1-under 69, maintaining sole possession of second at minus-11.
Sharing third place at 8-under-par 202 were Patrick Reed -- who had the low round of the day with a 6-under 64 -- Nicholas Thompson (66) and Scott Stallings (67).
Eric Meierdierks (66) notched a hole-in-one on the par-3 eighth, climbing into a share of sixth at minus-7 with Phil Mickelson (65).
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