Oosthuizen looked likely to miss the cut when he opened with a 77 playing alongside Tiger Woods and Rickie Fowler, and the threesome were a combined 28 over par for the first round.
The South African then bogeyed the first two holes of his second round to slip to nine over, but he rallied to post a sparkling 66 to make the cut with plenty to spare.
Oosthuizen carried on where he left off on Friday, returning another 66 on day three which included five birdies and just one dropped shot at the 11th, and that gave him a record total of 132 for the middle two rounds, beating the previous best of 133 held by Loren Roberts, Jim Furyk and Lee Westwood, and the clubhouse lead on one under par.
“Being nine over through 20 holes, it looked like I would have been back in??Florida today,” Oosthuizen said. “But I made a few putts yesterday and started??hitting the ball really well.
“I found a bit of a swing with my driver on the range and seemed to sort of go??from there on the rest of my game. And today I hit it really close on a lot of??holes, could have been probably a lot lower.
“I think all three of us pulled each other down into the depths a bit (on??Thursday). Everything was poor but I made one or two putts, had a great back??nine yesterday and built from there.”
But as Oosthuizen was on the rise, Phil Mickelson will have to wait another year for his next attempt at completing a career grand slam after tumbling out of contention with a seven-over 77.
The six-time runner-up, who shot 69 in the opening round, carded nine bogeys and two birdies to lie 10 over par and he said: “As bad as my score was, I hit a lot of good shots that ended up as bogeys and through three rounds I haven’t made a double.”
Meanwhile, Ian Poulter was reluctant to air his views on the Chambers Bay course after battling to a mixed-bag of a 69 which featured six birdies, three bogeys and one double-bogey.
“It’s tricky, but it’s playable,” the Englishman told Sky Sports 4. “But you can’t say what you would really like to say because there’s just no benefit in that. It’s hard to express yourself.”