Jordan Spieth knows, as should we, that he can't repeat 2015

At a tournament like the U.S. Open, where fairways and greens are at a premium, Jordan Spieth found the short grass only 50 percent of the time off the tee and hit just 56 percent of the greens in regulation for all four rounds. Sam Greenwood/Getty Images

OAKMONT, Pa. -- At the end of 2015, when Jordan Spieth was still riding high and soaking up some well-deserved adulation after one of the best seasons in golf history, Rory McIlroy -- the man who had his No. 1 ranking snatched away by Spieth -- made a prediction on how 2016 might go.

"It will feel completely different for Jordan," McIlroy said. "If you look at the stats at how those who have had a double-major season have performed the next year ... well, it's hard to back up. It just is. There's so much expectation, so much attention and focus, and I think it is more self-inflicted pressure, really, as your expectations are so high."

As Spieth walked up the 18th fairway of Oakmont Country Club on Sunday, several hours ahead of the leaders and wrapping up a T-37 finish, McIlroy's words seemed especially prophetic. This was a lot different than last year's U.S. Open, where Spieth was on his way to making the winning birdie putt at Chambers Bay. Sunday's finish snapped his streak of five straight finishes in the top four at a major. The only other players to do that since 1959, the year the PGA Championship went to stroke play, are Tiger Woods and Jack Nicklaus.

Spieth gave a few tepid waves, offered up a polite smile when the crowd showered him with polite applause and wisely refused to acknowledge a woman in the gallery screaming, "Please have my babies, Jordan!"

Mostly, Spieth looked weary.

He looked weary all week, if we're going to be honest about it. Some of that was Oakmont and the way it vexed him. He failed to break par in any of his four rounds. He ranked 59th in driving accuracy and 57th in greens hit in regulation. But some of it was the weight of great expectations and all the stuff we now expect of him.

Last year, when Spieth won the first two majors and had a decent chance to win the other two, it seemed like he could do no wrong. It was good to be Spieth. He was the new Golden Boy of golf, the first superstar after the Tiger Woods era to come from the United States. He was polite, charming and funny. He seemed authentic. He was a maestro in a press conference and just as good on the greens.

It's still good to be Jordan Spieth; it's just not as easy.

Total adulation is not everlasting, as LeBron James and Tom Brady and Woods could certainly attest. (McIlroy, as well.) Complexities emerge. It's hard to please everyone, and it's hard to live up to a ridiculously high standard you set for yourself. Some of the stuff that once seemed charming about Spieth -- talking to his ball every time it's in the air; having lengthy conversations with his caddie before each shot; answering question using the royal "we" -- are now the fuel for a small backlash. It isn't major, but it's there. You could feel it simmering in recent months. All you had to do was plug "Spieth" and "slow play" or "Spieth" and "slump" into Twitter's search engine.

Initially, Spieth seemed a little stung by the criticism. He barked at one of his haters on Instagram and tweeted in frustration at the PGA Tour's social media account when he didn't like a quote (of his) they used to promote a story. Several times, he got visibly annoyed at the suggestion he might be slumping in the months leading up to the Masters. The joy and whimsy that surrounded his 2015 season slowly evaporated. He seemed to grasp, for the first time, that his every move, his every word, his every missed shot, was going to be scrutinized.

We've seen a more guarded version of Spieth this season, and that's understandable. When he finished with his final round at Oakmont on Sunday, he paused to answer a few benign questions from the USGA pool reporter, then he ducked into the clubhouse and disappeared from view. There was some confusion over whether he was told by the USGA that reporters were waiting outside, hoping to interview him, but his agent soon sent back word he was declining to talk.

It wasn't a particularly good look: the defending U.S. Open champion and arguably the game's biggest name, brushing off the media after a mediocre showing at a major. But let's give Spieth the benefit of doubt. In the aftermath of the Masters, when he jumped out to a big lead the final day and lost by hitting two balls in the water on the 12th hole, he relived the horrors of that meltdown in intricate detail with reporters. It's hard to believe he would stick around for that mess, but then storm out of Oakmont Country Club after shooting 75.

What Spieth does seem to grasp, and what we should as well, is that it will never be 2015 again. He might win two (or more) majors in a single season again, but if he does, it will feel different. Nicklaus and Woods reinvented and rededicated themselves several times during their careers. Tiger changed his swing; Jack slimmed down. Tiger changed his coach; Jack grew warmer toward fans and other players with age. Both learned to be the face of the sport and how to shoulder that burden.

Spieth will likely adjust and reinvent himself, as well. We're now into the second act of his career. It just got even more interesting.