A Ryder Cup has broken out at the 2019 Open Championship at Royal Portrush. The top of the leaderboard is littered with former Ryder Cup golfers on both the European and American teams, and it makes for what should be a terrific final three days.

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J.B. Holmes is (improbably?) your leader after shooting a 5-under 66, but he's going to be hunted by some of the biggest dogs in the game over the final 54 holes. There are a few monster names who have played their way out of the tournament -- Rory McIlroy shot 79 and Tiger Woods shot 78 -- but plenty of stars are still in the mix as we wrap up the first day of play at Portrush. 

Here's a look at the leaders after 18 holes at the last major of the season.

1. J.B. Holmes (-5): Holmes summed up his strategy well after his round when he said playing a place like Portrush forces you to hit away from pins often and you just hope to hit a few putts. Holmes got plenty of looks after hitting 83 percent of greens in regulation. Maybe the most impressive part of his round? He bogeyed the first and played the next 17 in 6 under.

2. Shane Lowry (-4): While the day was not a great one for some Irishmen, it was good for Lowry. His 67 looked as if it might be a bit better as he got to 4 under through 12 holes, but he couldn't manage anything over the last six. He parred his way home for the early clubhouse lead before Holmes clipped him late. He's been quietly great recently with three top 10s in his last five starts. 

We'll split the T3s into some different categories since there are so many of them at 3 under.

T3 Heavyweights -- Brooks Koepka, Webb Simpson, Sergio Garcia, Jon Rahm: Everyone here except for Garcia shared the lead at one point in the day. Obviously, Koepka is the one who catches the most eyes, and he was tremendous, but I'm blown away by the ball striking of all four of these guys. They all seemed to be in complete control from tee to green in Round 1 and all but Rahm have at least one major. The four combined for just seven bogeys on the day, and Rahm had three of those (two in the last four holes!). If you fast-forwarded this thing to Sunday and told me one of these was the winner, I wouldn't even blink, although I would warn you that only two golfers -- Woods at Augusta and Gary Woodland at Pebble Beach -- have beaten Koepka in the last four majors. 

T3 Contenders -- Tyrrell Hatton, Lee Westwood, Tony Finau: This is an intriguing crew. I would be surprised if any of these guys won on Sunday for a variety of reasons, but they're all tantalizing. Westwood for what it would mean to win a dang Open at that age. Finau because it would be the fulfillment of his laugh-out-loud talent. And Hatton because an Englishman hasn't won since Nick Faldo in 1992. At least one of these three will be in it until late on Sunday.

T3 Pretenders -- Ryan Fox, Alex Noren, Dylan Frittelli, Robert Macintyre, Kiradech Aphibarnrat: I'm not (yet) a believer. Hey, they're all solid professional golfers, but Open winners in this field in this year? Noren is probably the most accomplished, but he's been mostly rubbish in 2019. Aphibarnrat is the most intriguing, but he's never had a top 10 at a major. The rest are mostly unknowns on this stage who could make for good fun should they hang around for another 36 holes or longer.

T16. Justin Rose (-2): Remember last Open when he barely made the cut then nearly won the tournament? If I'm leading the tournament, I'm pretty wary of where Rose is at all times. 

T20. Rickie Fowler, Patrick Cantlay, Jordan Spieth, Jason Day (-1): My (new) pick to win is coming from out of this group, and it's not Spieth, Day or Fowler. 

T42. Justin Thomas (E): He fought so hard to get it back to par after starting 3 over through four holes. Impressive last 14 holes after it looked like he was going the way of Rory.

T128. Phil Mickelson (+5): His six-day fast helped him beat two guys with a combined 18 majors! Unfortunately he's also probably still going to miss the cut. 

T144. Tiger Woods (+7): This ... does not seem good!

T150. Rory McIlroy (+8): I watched the entire thing, and I'm still astonished to see it on my screen.

CBS Sports was with you the entire way Thursday updating this story with the latest scores, analysis and highlights from Round 1 of the 2019 Open Championship. If you are unable to view the updates below, please click here.

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