The New Zealand golfer Danny Lee has dropped from 6th into a tie for 17th after the third round of the latest PGA tour event in Texas.
After rounds of 66 and 69 Lee carded an even par 70 to remain at five under for the tournament.
The American Kevin Na sank a 14-foot birdie putt on his penultimate hole on day three to break clear of a tie at the top with England's Ian Poulter and edge a stroke in front.
Na, who had been two ahead overnight in pursuit of a second PGA Tour victory, fired a one-under-par 69 in overcast, blustery conditions at a rain-softened Colonial Country Club to post an 11-under total of 199.
Poulter, seeking his third win on the U.S. circuit, missed a birdie attempt from seven feet at the par-four last and had to settle for second after returning a 68.
Australian Adam Scott, who won last year's tournament in a playoff, was five strokes off the pace after shooting a 66, ending the day level with Masters champion Jordan Spieth (67).
Due to threatening weather, the players set off earlier than scheduled in threesomes with a two-tee start.
Similar conditions have been forecast for Sunday with players again teeing off early in threesomes.