South African Louis Oosthuizen finished strongly in the third round of the Shell Houston Open to take a two shot lead into the clubhouse.

Oosthuizen couldn’t have had a worse start after bogeying both of the first two holes, but he went on to birdie five of the last seven to return a 6-under 66 to extend his lead to two shots.

"I had to compose myself," Oosthuizen said. "Other than that, I hit it well and started making a few putts on the back nine.

"I was driving it well, my iron play the whole week has been really good and I just made some good putts today.

"The greens here are really fast, which I enjoy. If it's not windy here, you feel like there are a lot of birdies out there."

American Hunter Mahan was alone in second place after carding a 65, with Carl Pettersson and halfway leader Brian Davis in third on 14 under.

For the second round in a row, players were allowed to lift, clean and replace their balls because the course had been saturated by rain.

Defending champion Phil Mickelson was among a group of three players tied for sixth on 11 under.

Els trying to qualify for the Masters

Three-times Major winner Ernie Els, who needs to win the Shell Houston Open to qualify for the Masters, was at eight-under after shooting a second successive 69.

"I've just got to stick to what I'm doing," Els said. "I'm playing really well.

"Obviously, I would love to get a win. I'd like to play a solid round of golf tomorrow. If it really gets going, that will be really a plus."