Mahan, who came into Saturday's third round with the lead, bowed out when informed that his wife had gone into labor with the couple's first child, opening the door for Snedeker, who turned in a bogey-free effort at Glen Abbey Golf Club.
He ended 54 holes at 14-under 202, one stroke better than David Lingmerth, who eagled the 18th to finish with a 7-under 65.
John Merrick, who inherited the lead when Mahan withdrew, carded an even-par 72, dropping into a fifth-place tie with Dustin Johnson (63), Charley Hoffman (67), Kyle Stanley (66) and Greg Owen (67) at minus-11.
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