Atwal, lying second after the second round at 10-under, is now eight-under 205 and tied 24th.
Atwal was hit by closing woes as he was fine at one-under through 12 holes, before dropping shots on 13th, 14th and 18th to finish at 73.
Meanwhile Lefty Edward Loar of Dallas fired a 7-under 64 and moved into the lead after 54 holes at 15-under 198 total. Loar, who tied for second at the Chile Classic two weeks ago, is one ahead of Troy Merritt (66) and two in front of Morgan Hoffmann, who decimated the Le Triomphe Country Club with a 9-under 62.