FARMINGDALE, NY -- A week that we thought would belong to a big, burly brawler like Brooks Koepka, Dustin Johnson or Rory McIlroy might just end up going to the biggest fighter of them all, Jordan Spieth. The three-time major champion shot a 4-under 66 on Friday in Round 2 of the 2019 PGA Championship to get to 5 under for the week and solo second place at the time he finished his round. It was his second straight round in the 60s and put him in unfamiliar territory in 2019.

Spieth doesn't have a top-10 finish since the 2018 Open Championship.

Spieth started on the back nine and went out in a pedestrian 35, but he did his work on the front nine of the course. It started with a 20-foot birdie putt at the 1st and continued with short birds at the 4th and 7th. Then he got away with one -- a 40-footer -- at the par-4 8th and made par at the 9th to close in 31. He's played that side of Bethpage Black in 6 under so far this week.

It wasn't the birdies that impressed, though; it was the dearth of bogeys. Spieth has been scoring all season, but he's also been giving it back. He came into this week T148 in bogey avoidance on the PGA Tour this year. He's only made two in his last 24 holes this week.

The concern -- if there is one for somebody who's 5 under through two rounds at Bethpage -- is that Spieth has leaned too heavily on his putter. He's second in the field in putting so far this week 76th on approach shots. The obvious question is whether that's sustainable with the pressure and potentially the firmness of this tracked turned all the way up.

There's another bit of pressure Spieth said he hasn't thought about yet. With a victory this week at Bethpage, Spieth would join Jack Nicklaus, Ben Hogan, Gene Sarazen, Tiger Woods and Gary Player as the only six golfers to ever win all four majors in a career.

"[Winning the career grand slam] tells you your game travels anywhere and can win the biggest events on any type of course in any situation," said Spieth earlier this week. "Each one has its own identity, each major championship, and so you've kind of ... mastered golf is kind of an easy way to say it, if you're able to complete a career grand slam."

Thankfully for Spieth, this week Bethpage is playing less like a PGA Championship and more like a U.S. Open, which highlights the wealth of strengths Spieth possesses. 

"PGAs change a lot," he said this week. "Out of all four of the majors, they're probably the most difficult I've found for my game to translate to. But any given year it can certainly play like a U.S. Open as far as the difficulty level, and it can play kind of as fast as an Open Championship, depending on where you are."

That's certainly where we are with the current 36-hole scoring mark after the Friday morning wave set by Spieth at 135. There will be no running away to 20 under, no four-straight 65s. This thing will be a bloodbath until the very end, and that's normally good news for somebody like Spieth who beats you with his mind and his will more than he beats you with his driver and his putter.

I don't want to overstate those last two points because certainly everyone still left in the field is grinding to finish as high on the PGA Championship leaderboard as possible. But the particular way in which Spieth's struggles have played out over the past year or so has been equal parts hard to watch and fascinating. He is so intent on figuring out the minutia of his swing that he seems to be trying to talk himself into how good he had been just a couple years ago.

The problem for him now is going out and proving it with the heat cranked in Rounds 3 and 4. Spieth is No. 3 on the PGA Tour in second-round scoring average. He has rounds in the 60s in 11 of 13 second rounds ... but he's 193rd in Round 3 and 208th in Round 4. It sounds strange to say this about a three-time major winner, but there's a lot to prove over the next 36.

There's also a lot to gain. Spieth can simultaneously escape the claws of whatever it is that's been gripping his mind and his driver over the last few months and graduate from current great to all-time legend with two more good rounds.

"I haven't been in contention on a Sunday since The Open last year," said Spieth on Friday. "If I'm able to put some good work in tomorrow, then ... I will be in contention on Sunday. And at that point, it will be just more of trying to win a golf tournament. It won't matter to me what tournament it is. I'll be pleased to be in contention, knowing that the work I put in from being pretty far off has really come back nicely on a very difficult golf course.

He'll have to thwart Brooks Koepka, who he's still looking up at on the board and Dustin Johnson, who trails Spieth by just one.

And if the fight was a real one, I would not put money on the Texan. This one plays out not in a gym or a street but rather in the place where Spieth has courted and won so many battles over the course of his still-young career, between the fairways, on the greens and in the space that always-active brain occupies. Odds will still be on Koepka and Co. But maybe money should be on Spieth.