FARMINGDALE, N.Y. -- Brooks Koepka was in one of the early groups out on the course at Bethpage Black in the 101st PGA Championship, so his course-record 63 lingered over the rest of the field as everyone tried to chase the defending champion and clubhouse leader's early advantage at 7 under. By the end of the afternoon only one player, Danny Lee, was within three strokes of Koepka. 

It's difficult to know where you draw the line for real contention after just 18 holes of action, particularly at a course where bogeys and double bogeys seem to lie in waiting at every turn. Dustin Johnson, Jason Day, Jordan Spieth and Phil Mickelson are all in the top 10 on the leaderboard technically, but that top 10 doesn't feel as close to the top when the leader is up six strokes heading into Friday. 

The largest comeback to win we've seen in PGA Championship after 18 holes was eight strokes, so in theory, there are 52 golfers still within that comeback precedent. Tiger Woods, at 2 over, is not included in that group. Woods started his day with a double bogey and spent much of the early round grinding with few birdie opportunities. When he got good looks, he was able to take advantage and found himself moving with some momentum after back-to-back birdies. 

Woods had some mistakes coming down the stretch and a few missed putts that strayed from what had been solid form on the greens to that point. Overcoming a nine-stroke deficit requires Koepka, Lee and others to fall back a few strokes, but it also requires Woods to play much better than he did on Thursday. 

With just 17 players under par, a big winner on Thursday was Bethpage Black itself. Koepka and Lee may have come out unscathed, but it's unsustainable to expect those same results the rest of the week. When the setbacks come, the leaders are going to be required to have a championship caliber response in order to keep this cushion on the rest of the field. 

Here's how the top of the leaderboard looks after the first round: 

1. Brooks Koepka (-7): There's a little bit of creeping dread considering the idea that Koepka ended the PGA Championship just five hours into the proceedings. Not only is Koepka the best major competitor in the world, he just might be the best player in the world. And now he's got a hot putter and a comfortable lead over most of his usual rivals in these competitions. The only uncertainty that I can consider for Koepka is the long layoff from Thursday morning and the possibility of tougher conditions tomorrow afternoon. 

2. Danny Lee (-6): It was a scrambling 64 for Lee with eight birdies and two bogeys while missing nearly half of his greens in regulation. Lee is a grinder, so this kind of play on the big stage is encouraging for the one-time PGA Tour winner. 

3. Tommy Fleetwood (-3): There were a couple of huge par saves for Fleetwood on a day where he was able to take advantage of scoring opportunities. He started his day at the difficult 10th hole with a bogey and then held things together for a few holes before back-to-back birdies on 15 and 16 got him rolling. His second nine -- the front nine at Bethpage -- was a bit more erratic with four birdies and two bogeys, but in general, Fleetwood has to be feeling good about his round and where he sits on the leaderboard.   

T4. Mike Lorenzo-Vera, Luke List, Sung Kang, Chez Reavie, Pat Perez (-2): In just his second PGA Championship appearance, Lorenzo-Vera started the tournament with elite play on and around the greens. He ranks in the top 10 in the field in strokes gained putting, fared well in the sand and went bogey-free on the back nine with two birdies on 16 and 18 to finish his 68 on a high note. Reavie played the handbook beautifully for success at Bethpage with 85.7 percent driving accuracy. Perez did the exact opposite with 42.8 percent driving accuracy. Both sit T5 on the leaderboard after shooting a 68 in the first round. Golf!

T9. Rickie Fowler, Dustin Johnson, Jordan Spieth, Phil Mickelson, Jason Day, Si Woo Kimm, Matt Wallace, Patrick Cantlay (-1): Not all 69s are alike, especially with this group. For some, like Spieth, shooting a 69 feels great. He's been grinding to get his game back in condition to contend for major championships, and he had to throw four birdies on the card to make up for the three strokes he gave up between the 10th and 12th hole. Johnson, on the other hand, sees all the missed putts and thinks of how much lower that round should have been after leading the field in driving and hitting nearly every green. When you consider the quality of golfers here in this group at 1-under, it's safe to say this is probably the limit of where we might find our champion.

T52. Tiger Woods, Rory McIlroy, 20 others (+2): For the Woods the disappointment can be isolated to a few missed putts, bad shots and mistakes. But after hitting nearly every green in regulation, McIlroy's frustrations are more consistent through the round and focus on his putter. McIlroy ranked T-115th in putting accuracy and 114th in strokes gained putting, which all but negated his performance off the tee which ranked second in the field.  

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