Former British Open champion Louis Oosthuizen birdied five of the last seven holes to charge two shots clear in the third round of the weather-delayed Houston Open in Humble, Texas on Saturday.
The smooth-swinging South African recovered from bogeys on the first two holes to card a six-under-par 66 at the rain-softened Redstone Golf Club in the final PGA Tour event before next week's Masters.
Oosthuizen, who romped to a seven-stroke victory at the 2010 British Open, launched his late surge with four consecutive birdies from the 12th to post a 17-under total of 199.
American Hunter Mahan was alone in second place after carding a 65, with Swede Carl Pettersson (67) and Britain's Brian Davis (69) a further stroke back at 14 under.
Defending champion Phil Mickelson was among a group of three players tied for sixth at 11 under after shooting a three-birdie 70.
For the second round in a row at Redstone, players were permitted to lift, clean and replace their balls on a course that had been saturated by more than an inch of rain on Thursday.
Earlier in the day, American Jeff Maggert birdied three of his last eight holes to grab a one-shot lead when the weather-delayed second round was finally completed at Redstone to get the tournament back on track.
Maggert went on to shoot 76 in the third round to finish a long day tied for 14th at eight under par.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Larry Fine)