Clark, 32, completed 54 holes at 5-under 205. This is only the second time he has held the 54-hole lead.
Clark will be gunning for his first PGA Tour win Sunday. He is the PGA Tour's career money leader without a win, with earnings of nearly $10.7 million.
Gavin Coles and Marc Turnesa, two of six second-round leaders, both shot 70 and dropped a into tie for second at 3-under 207 with Masters champ Trevor Immelman (67), Bill Haas (67) and Alex Cejka (69).
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