I'm loving the fact I'm playing absolutely great golf, Phil Mickelson

Phil Mickelson (FSY), who had a chance at the start of the week to go to No. 1 in the world, was another shot behind. Whatever momentum he had was lost with a 5-iron that he hooked out-of-bounds for a double bogey on No. 16 for a 70.

The South African heritage at golf's oldest championship dates to Bobby Locke winning four times in a nine-year stretch after World War II. Player won the claret jug three times, and Els was the most recent in 2002.

Oosthuizen, whose career was made possible by the Ernie Els Foundation at Fancourt, recalls watching highlights of the Big Easy's tough win at Muirfield and getting goosebumps.

All he felt on the first hole Saturday were nerves.

He had to wait 28 hours from his last putt on Friday to his opening shot Saturday — "It felt like a week-and-a-half," he said — and Oosthuizen promptly three-putted for bogey as his lead shrunk to two shots. Considering it was only the second time he made it to the weekend at a major, it looked as though it wouldn't be long before he wilted from the pressure.

Instead, he eased his way along the humps and mounds, flashing that gap-tooth smile and following Els' advice to enjoy himself. Oosthuizen picked up his first birdie on the seventh hole, then added a surprise birdie late in his round with a 60-foot putt.

Even with a four-shot lead — the largest 54-hole lead in the Open since Woods led by six shots in 2000 — the real test comes Sunday.

"I'm loving the fact I'm playing absolutely great golf and I'm four shots being Louis," Casey said.

Casey ran off three birdies in a four-hole stretch early in his round, and he got as close as one-shot with a two-putt birdie on the ninth. But he had to settle for nothing better than par on the back nine, missing a 5-foot birdie on the 18th.

"I'm having a great time, and I'm going to go out there tomorrow and enjoy myself and have a good attitude," Casey said. "I know what this golf course can do. It can give you some great moments, and it can give you some horrible ones."

A few weird moments, too.

Miguel Angel Jimenez (FSY) added another highlight to the infamous Road Hole when he turned his back on the green and banged a shot off the waist-high wall, where it caromed back over the road, up a slope and onto the green.