"Other than that, really happy with how I hit it and fought back after a pretty tough start. I feel pretty comfortable with every part of my game."
Fellow Kiwi Daniel Hillier failed to make the cut after a one-over second round left him sitting at three-over par for the tournament, two shots off the cut.
At the top of the leaderboard is Oosthuizen, who set a 36-hole record at the British Open and is halfway to ending his run of near misses at the majors.
Now all he has to do is hold off a cast of major champions at Royal St. George's.
On a day of pleasant weather that took the fear out of the links off Sandwich Bay, Oosthuizen broke away from a three-way tie with a birdie-birdie-eagle run from the 12th hole. He shrugged off his first bogey of the week for a five-under 65 and a two-stroke lead.
Former PGA champion Collin Morikawa had a 64 in the morning and was two shots behind. Another shot back was Jordan Spieth (67), going after his fourth major. Lurking was two-time major champion Dustin Johnson, the No 1 player in the world who shot 65 and was tied for fourth, four strokes behind Oosthuizen.
"The game is good, but I know it's a really good leaderboard," Oosthuizen said. "I'll have to play good golf this weekend if I want to come out first."
Oosthuizen, looking as calm as the conditions, was at 11-under 129, breaking the 36-hole Open record first set by Nick Faldo in 1992 at Muirfield and matched by Brandt Snedeker in 2012 at Royal Lytham & St. Annes.
This will be the fifth time in the last nine rounds at a major that Oosthuizen, the 2010 Open champion at St. Andrews, has had at least a share of the lead. He was runner-up at the last two majors, to Phil Mickelson at the PGA Championship in May and to Jon Rahm the US Open last month.
"I'm not really going to think about the second spots," said Oosthuizen, when asked what he'll do differently this time. "I know my game is in a good place."
He'll also be aware of the quality of player behind him, though.
Morikawa, making quite a debut in major links golf, made seven birdies in his first 14 holes as part of a clinic in iron play. He missed a five-foot par putt on No. 15 — ending a 27-hole stretch without a bogey — and had a 10-foot birdie putt on the final hole catch the lip.
Spieth, four shots behind Morikawa when he teed off, was tied for the lead after 12 holes and then played the last six holes in one-over, a stretch he described as "frustrating."
Then there was Johnson, a runner-up at Royal St. George's in 2011, who stuck his approach at the last to three feet for a birdie and a round of 65, which left him at seven-under with Dylan Frittelli of South Africa (67) and Scottie Scheffler (66).
The weather is expected to stay benign over the weekend, potentially favouring Johnson if the fairways firm up and the ball runs longer and faster.
One shot behind an eclectic mix of players at six-under — including two more South Africans in Justin Harding and Daniel Van Tonder as well as Germany's Marcel Siem, who qualified from a second-tier Challenge Tour event last week — were Rahm (64) and Brooks Koepka.
Koepka, a four-time major winner and seemingly always in contention at golf's biggest events, made four birdies in his last five holes for a 66.
- With AP
