The symmetry was close to perfection. As Tiger Woods teed off from the first tee, his fellow Swoosh embroidered golfer was some 60 yards away prowling the ninth green as he lined up a 15-foot birdie putt.

For much of the day, Rory McIlroy had made this season's two other Major champions, Bubba Watson and Martin Kaymer, the other two members of his group, appear like minor beings. Now, he had the chance to finish his second round in style.

And he did. Watson remained expressionless. Kaymer smiled. Further away, Woods and those other members of the marquee group of the second wave – Pádraig Harrington and Phil Mickelson – were left in little doubt of what had happened.

Having watched as Kaymer’s own birdie putt veered to the left, which left the German missing the cut, McIlroy coolly assessed his own line and read it perfectly, the right-to-left putt falling into the tin cup. The noise which greeted McIlroy’s 67th stroke of the day made its way back towards the first tee.

Birdie machine

On the green itself, McIlroy produced his trademark fist pump into the air as the ball disappeared. He is a birdie machine these days. That closing birdie – timed beautifully – made for quite the statistic. In McIlroy’s last ten competitive rounds of 2014, he is 41-under par – nine-under-par for the first two rounds here at the

US PGA

; 15-under-par in winning the WGC-Bridgestone Invitational, and 17-under-par in winning the British Open.

On the eve of this championship, Darren Clarke had made the analogy that his fellow-Northern Irishman was, as he put it, "like a runaway train . . . . unstoppable!"

Maybe somewhere along the line, someone will manage to snag him. Up to now, however, McIlroy has performed with all the splendour of a Rolls Royce.

His driving, in particular, has been sublime. At one point of yesterday’s second round, he produced five successful drives – on the 16th, 17th, 18th, first and second – in excess of 300 yards. Watson was drawn into a war he couldn’t win.

And, as Kaymer, the US Open champion, admitted afterwards: “You just have to respect it a lot, how good he plays. There’s nothing wrong with his game. Putting. Chipping. Bunker, whatever it is. And he hits it 20, 25 yards longer than anyone else. He’s definitely the best player in the world.”

In all, McIlroy had an eagle, four birdies and two bogeys in manoeuvring his way towards the lead. It wasn’t entirely plain sailing. On the 12th, his three-wood off the tee found the left rough. “I had to turn it around the edge of an overhanging tree.” He found the front greenside bunker, where the sand had compacted. “It’s hard to slide your club underneath the ball, it was a tough up-and-down.” He didn’t make it, registering his first bogey.

But, as he did on Thursday when recovering from a double-bogey and bogey start to the back nine of holes to cover the stretch from the 12th to the 18th in five-under, McIlroy bounced back again yesterday.

Lob wedge

A lob wedge approach to the 13th green to 12 feet set up a birdie. And, on the 15th, he hit an eight-iron approach from rough to 20 feet and converted the birdie.

His play of the Par 5s was the real foundation: on the 542 yards 18th, his ninth of the day, McIlroy – after a drive of 311 yard – hit his four-iron approach to 30 feet to the front edge of the green and rolled in the uphill eagle putt.

A bogey on the second hole came as a wake-up call. His approach found a greenside bunker. His recovery finished ten feet from the hole. He missed the par putt.

Payback came on the 597 -yard seventh hole, as he hit a great drive down the fairway and short of the water hazard. With 242 yards to the flag, McIlroy asked his caddie JP Fitzgerald for the five-wood and produced the best shot of his round. With a high ball flight, the ball appeared to hang in the air for an eternity before falling to earth some eight feet from the pin.

Bombing drives

“I didn’t trust the read on the putt,” he admitted. He pushed it, and although the eagle chance disappeared, he tapped in for a birdie to regain the lead.

On his finishing hole, the ninth, he hit a five-wood off the tee and a nine-iron to 15 feet. “It was nice to birdie a couple coming in,” admitted McIlroy.

Yet again, McIlroy’s booming drives – to soft fairways – set him up to take advantage of the course.

“Yeah, I still like bombing drives 350 down the middle,” admitted McIlroy

“I think that’s when my confidence grows. When I see good shots like that and I see drives down the middle and tarring iron shots into the greens, that’s the way I like to play.”