PGA is a test for all, but most of all Rory McIlroy

The short list of things golf followers thought they never would see: Adam Scott finally winning a major championship, the tiny old Merion course totally overwhelming powerful modern golfers (with Justin Rose finally winning a major) and Phil Mickelson mastering links golf and winning the British Open.

One after another, the major championships of 2013 have brought results that were somewhere between improbable and impossible. That makes you wonder what the sport might have up its sleeve this week, in the final major. A win by the defending champion, Rory McIlroy, might be the most surprising finish of all.

It has been an eye-opening year for the game that enters the PGA Championship at Oak Hill in upstate Rochester. It has been an eyesore of a year for McIlroy, who appeared on top of the world -- and headed even higher -- a year ago.

Through Saturday's round at the WGC Bridgestone Invitational, McIlroy was an aggregate 10 over par in 14 stroke-play events this year. He sure has looked and sounded like a different guy than the one who was No. 1 in the world, having breezed to an eight-stroke victory at Kiawah Island last August.

Since then, he has received criticism and / or advice about his equipment change (reportedly a nine-figure deal from Nike), his commitment, his loyalty to his friends and management team and his love life.

Nick Faldo has said McIlroy "messed with a winning formula" by changing all of his equipment and following Tiger Woods into the Nike stable. Jack Nicklaus noted that McIlroy no longer was "grinding, grinding, grinding to get where he wanted," although he did add that McIlroy is "too talented, too hardworking, too good a kid to not get it back."

Most recently, Gary Player, a 77-year-old who has been married for 56 years, said McIlroy needs to find "the right wife."

The latter could have been a swipe at the Northern Ireland golfer's girlfriend, tennis pro Caroline Wozniacki, but McIlroy, 24, chose not to fire back. At the Bridgestone this week, he claimed not to have heard Player's comments and said only, "All I know is I've got a lot of respect for the man and he's someone I definitely look up to."

At any rate, the most disconcerting comments about McIlroy might have come from the player's own mouth. During the British Open at Muirfield, he said, "Sometimes I feel like I'm walking around out there and I'm unconscious. I just need to try to think more . . . I can't really fathom it at the minute."

One source of his troubles is the competitive level of pro golf. There is no time or space for a top player to switch gears or catch his breath. Elite players are hungry for breakthroughs, as Scott and Rose were at 32. A star such as Mickelson can shake off a devastating defeat (at Merion) and break new ground (Muirfield). Others are desperate to have their day (Lee Westwood, Luke Donald, Jason Day). And don't forget Tiger's major quest.

McIlroy recently spent a few weeks at home, playing golf with buddies. "It makes you realize why you started, because you love the game," he said at the Bridgestone.

He takes encouragement in the fact that he was struggling before the PGA last summer, too, and in the fact that, this year, anything can happen in a major.