US Open Second round:The conqueror walked off the final green, in his case the ninth, to a gallery of his peers. Some doffed their caps to Paul Casey, others gave him the thumbs up sign. Others applauded.

Colin Montgomerie and Chris DiMarco stood on the back of the green, which doubles as a practice putting area, and simply looked bemused by what the Englishman had achieved, a round of 66 on a course with all the sticking ability of a pane of glass. He had achieved the nigh impossible.

In catapulting up the leader board, bettering his first-round effort by 11 shots, Casey had undergone something of an epiphany. "This is right up there in terms of my best round ever. I consider the US Open to be the toughest test in golf and this is probably the toughest course I've ever played. I feel very, very lucky to have shot 66 on it. I've shot lower numbers. I've holed out shots. But I'm just ecstatic with that," he remarked.

The transformation from his first round was pretty remarkable, and Casey - hardly a shrinking violet - even felt a tinge of discomfiture that his fellow tour players and their caddies should react in the way they did. "I don't like playing in front of my peers. It is one thing if you're in a group and playing with the guys. But when they stand around and watch, I feel like everybody's critiquing," he explained.

Still, he couldn't but enjoy the moment. Nick Dougherty, the first-round leader, walked off the putting green on his way to the 10th tee to start his second round and gave Casey a thumbs-up salute. Ricky Barnes did the same. It was then Casey looked up to see Montgomerie and DiMarco standing like statues. "I saw Monty and Chris, sort of shrugging their shoulders and giving me that "how-on-earth-have-you-shot-that" sort of look, which I returned."

On Thursday evening, Casey had hit the range after an opening round 77. For much of last week, he had worked with his coach, Peter Kostis, and felt invigorated heading to Oakmont. In practice on Wednesday, he shot a 69 playing with Sergio Garcia and Luke Donald. He felt very good. Then, in that first round, it all went wrong; and brought back memories of the Masters at Augusta where he shot himself in the foot with an opening round 79. The problem?

"I was a little wrapped up in technique," he explained. "If I swing the club correctly, then surely the ball is going to go in the right direction. I went to the range and, after an hour figuring that out, I walked off the range in frustration and started out well this morning and got back to what I do best, which is swinging the club. Just swinging the club, and not worrying too much about it."

It was a recipe that brought results, his round producing five birdies and just one dropped shot.

Casey had 10 single putts in a round that saw him use the putter just 26 times, and reinvigorated his challenge for the championship.

While Johnny Miller shot a final round 63 on the way to winning the 1973 US Open here at Oakmont, Casey's 66 was crafted on a course deemed to be playing the toughest in the history of the championship, with the greens again hard and firm with the softening effects of Wednesday night's thunderstorm undone by the return of sunshine and a breeze that dried the putting surfaces and returned them to the way the USGA wanted them to be.

Casey probably knew it could be his day from the moment he canned a birdie on the 10th, his first hole.

There, with an approach shot from 165 yards, the Englishman's eight-iron finished some 45 feet from the hole. But he holed the putt. "It probably would have gone 10 feet by if it didn't go in," he confessed.

His second birdie arrived on the 12th, where he hit a nine-iron approach to nine feet. When he hit his wedge approach to 18 inches on the 14th, his recovery was well and truly under way. And his fourth birdie duly arrived on the 17th, where he curled in a viciously breaking left-to-right putt from 15 feet.

If he felt invincible at that stage, a touch of reality was brought into the equation when Casey bogeyed the 18th, where he missed the green with his seven-iron approach shot and failed to get up and down. Thereafter, it was par golf with the exception of the seventh, where he holed a 15-footer.

His final act of the day was to tap-in from 18 inches for a par on the ninth, whereupon his peers on the practice putting area let them know their feelings.

Stewart Cink, who had played in the same group, wrapped his arms around Casey's shoulders. Cink was on the other end of a beating in the Saturday foursomes at the Ryder Cup when Casey finished off the match with a hole-in-one on the 14th, a shot which was "shot of the year" on the European Tour last season. He knew to expect the unexpected from Casey.

"I've never been afraid of shooting low numbers. I don't get scared of being a few under. I see it as a challenge," he said. "But I also have the possibility of going the other way, so I've learned to have a little bit of discipline. But, when it's on, I can't resist firing at the flags."

The challenge for Casey now, though, is to follow up his moving round with two solid rounds.