2010 Open Championship winner Louis Oosthuizen holds a two-shot lead over Hunter Mahan entering the final round of the Shell Houston Open. Oosthuizen carded a 6-under 66 on Saturday to lead Mahan (65) at 17 under at Redstone Golf Club.
Carl Pettersson and Brian Davis are at 14 under and tied for third place.
James Driscoll is alone in fifth at 12 under. Phil Mickelson, Keegan Bradley and Ryan Palmer are another shot back, tied for sixth.
John Senden, Boo Weekley, John Huh, J.B. Holmes and Tommy Gainey are the quintet in ninth at 10 under.
Ernie Els, who must win to get into the Masters for a 19th consecutive year, trails his fellow countryman by nine shots.