Seamus Power's run of poor third round form continued in Dallas when he bogeyed his last two holes in the AT&T Byron Nelson and shot a two over 72 to fall 27 places to tied 52nd on level par.
The West Waterford man is ranked fifth in first round scoring (69.07) and 53rd in round two (70.36). But he was 119th in round three (71.2) before today's round and 185th for round four (72.33).
Three three-putt bogeys did much of the damage for Power, who made four birdies and six bogeys at the TPC Four Seasons Resort.
Power is now 12 strokes behind James Hahn, who shot a six-under 64 to lead by one stroke on 12-under par from Billy Horschel (66) and by two from Jason Day (63) and Jason Kokrak (72).
Masters champion Sergio Garcia (64) is tied sixth on eight under, four behind with world No 1 Dustin Johnson (71) slipping from third to tied 19t on five-under.