Rory McIlroy's quest for back-to-back major titles hit an early stumbling block at the PGA Championship, as the Northern Irishman stumbled to a four-over-par opening round at Aronimink Golf Club in Philadelphia.

The 37-year-old, fresh off defending his Masters title at Augusta last month, was looking to become the most successful European golfer of the modern era by claiming his seventh major championship—surpassing Nick Faldo's tally. But instead of glory, McIlroy's round unraveled with four consecutive bogeys on his back nine, leaving him well off the clubhouse lead at three under par.

Starting on the 10th hole, McIlroy's day began with a bogey after he was forced to hack out of the rough. He quickly bounced back with a birdie at the 11th, setting off a streak of 10 straight pars. However, the momentum shifted when his birdie putt on the 18th agonizingly stopped short, leaving him bent double in frustration as his ball rolled back to the front of the first green.

The two-time PGA champion's struggles continued into the front nine. A wayward drive on the fourth led to another bogey, though he briefly recovered by sinking a 31-foot putt. But from there, it was all downhill. Inaccurate tee shots resulted in four straight bogeys, decimating what had been a promising round.

McIlroy was playing in a marquee group alongside Jon Rahm and Jordan Spieth, the latter chasing a PGA Championship win to complete the career grand slam. The massive galleries following the trio were treated to a mix of brilliance and frustration. Rahm's round mirrored McIlroy's early struggles, with a bogey on the 10th and another on the first after a spectator jokingly yelled, "Welcome to Aronimink, Jon!"

But the Spaniard's fortunes turned dramatically when his pitch from 98 yards hopped twice and dropped into the hole for his first-ever PGA Championship eagle, pulling him back to one under par—where he finished the round.

For McIlroy, the opening round is a setback, but with three more days of competition, there's still time to turn it around. The key will be finding consistency off the tee and staying patient on those challenging greens.