HUMBLE, Texas (AP) ― Louis Oosthuizen shot his second straight 6-under 66 on Saturday to reach 17 under and take a two-shot lead over Hunter Mahan after the third round of the Houston Open.

The 29-year-old South African shook off two early bogeys on a sunny, windy afternoon at Redstone. He reeled off four birdies in a row on the back nine to surge ahead.

“It’s a great leaderboard behind me,” Oosthuizen said. “It’s going to be tough, but I feel like I’m ready for it.”

Mahan had a 65, rebounding from a bogey on No. 9 with four birdies on the back nine.

Carl Pettersson (67) and Brian Davis (69) were three strokes back at 14 under. James Driscoll (71) was alone at 12 under. Defending champion Phil Mickelson (70), Keegan Bradley (69) and Ryan Palmer (66) were 11 under.

Three-time major champion Ernie Els, who must win to qualify for the Masters next week, was in a group at 8 under. Els hasn’t missed the Masters since 1993 and knew that his chances of winning Sunday are remote.

“I needed to get to 10 or 11 under to really have a shot,” Els said. “I need a 62 or 63. It’s tough to do on a Sunday, but you might as well give it a go.”

The tournament’s schedule was pushed back by a thunderstorm Thursday, and 70 players resumed their second rounds Saturday morning.