The 40-year-old Ryder Cup player was three shots off the lead at the halfway stage but a 74 leaves him six shots adrift.
American pair Jim Herman and Jamie Lovemark share the lead on 11 under.
Sweden's Henrik Stenson and Americans Dustin Johnson and Russell Henley are a further shot behind in the last event before the Masters.
Welshman Jamie Donaldson saw his chances of victory at the Houston Open fade after a poor third round.