Jordan Spieth is having a down year, well, for him anyway. He has as many missed cuts (five) as he has top-10 finishes, and he's only truly put himself in position to win one golf tournament (The Open) so far this summer. He's 38th in strokes gained overall, 165th in strokes gained putting and has slipped from No. 2 at the beginning of the year to No. 8 going into this PGA.

And yet ... Spieth has the opportunity to flip the script on his season and transform it from one of the most pedestrian years of his young career to one of the most successful and memorable in the modern golf era. How? Well, with four good rounds at Bellerive and the 2018 PGA Championship (airing live this week on CBS and CBSSports.com), Spieth could join Tiger Woods, Jack Nicklaus, Ben Hogan, Gene Sarazen and Gary Player as the only six golfers to win the career grand slam.

You might hear a few times this week that Player completed his slam with a U.S. Open win in 1965 on this very course.

The Wanamaker is the only one of the big four trophies that Spieth lacks, but a win this week would erase that. And then, 25 years from now, nobody would remember that he faltered late at Carnoustie or missed the cut at the U.S. Open or went a year without winning. They would only remember 2018 as the season when Spieth joined Rory McIlroy in the four-major club and made a whole lot of history in the process. 

The problem for Spieth is two-fold. First, golf has probably never been deeper or better -- there are about a dozen golfers who have never even won a major that would surprise nobody by winning this one. Second, he's not exactly trending in general or at PGA Championships. 

Much of Spieth's success over the course of his career has come at the Masters and Open Championship. His only great performance at the U.S. Open was a win at Chambers Bay in 2015, and his only great performance at the PGA Championship was a runner-up finish to Jason Day at Whistling Straits that same year.

Bellerive doesn't exactly scream, "Jordan Spieth will torch the field at this place," even though I think he has whatever it is a golfer needs to be able to do that at any given moment. It's a big bomber's paradise, and while Spieth is plenty long, he's not long in the way you need to be long to give yourself a distinct competitive advantage at this course. He's also coming in off a lousy WGC-Bridgestone Invitational in which he finished T60 and got beat by Alex Bjork, Ted Potter and Wade Ormsby.

The silver sliver here is that Spieth always seems to be able to conjure up what he needs at major championships. He's somehow been in the thick of it at two of the three, even though I'm not sure he's actually played well all season. A 64 that could have been a 60 in the final round at Augusta left him in third place but with a real chance at history for a while. He also played in the final pairing at The Open with Xander Schauffele before stalling out with a birdie-free 76 in defense of his Claret Jug.

So I'm not totally sure what to expect from the generationally great Spieth. Nothing much surprises me with him, but this win would be his first in over a year on a course that probably doesn't suit him all that well.

Regardless, it would be very Spiethian of him to grab this win in this week. After owning the top of the golf scene from most of 2015-18, he's recently taken a back seat to Justin Thomas, Dustin Johnson and a host of other players.

We remember singular moments, though, and he has a chance to deliver a great one at Bellerive: the slam. If he pulls it off where McIlroy (Masters) and Phil Mickelson (U.S. Open) failed, we will never remember how he got there or what he did thereafter. We will only remember 2018 as the year when Jordan Spieth was transformed from boy wunderkind to living legend.

So, who will win the 2018 PGA Championship, and which long shots will stun the golfing world? Visit SportsLine now to find out and see the full PGA Championship projected leaderboard from the model that has nailed four of the last seven majors heading into the weekend and was all over Tiger Woods' surprising run at the The Open Championship.