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After shooting rounds of 64 and 68 and finishing with four birdies in his five final holes at a Dallas qualifier in June, the 15-year-old Hammer became the third-youngest player to ever qualify for the tournament.
After the first round of the US Open, Hammer is tied for 135th place at 7-over. It's not a great score, even on the challenging Chambers Bay course. But it's still three shots better than Tiger Woods, who had a career-worst day at the Open.
On the first tee, cameras caught Hammer seemingly overwhelmed by the moment, crouched down and looking emotional:
Afterward, Hammer told reporters he was just praying and taking in the moment. He "wasn't emotional or anything," he says:
"I was just praying. I always pray right before my round on the first tee. And so, yeah, that's all I was doing. I wasn't emotional or anything... I don't even know, I mean, I've never felt that feeling, for sure, it was so different. But I liked it. It was kind of a different like kind of a sweet feeling to have. But, yeah, I can't even describe it."
Hammer comes across as a wide-eyed, happy-to-be-here kid, but he has golfing maturity beyond his years and is only gaining more experience at the Open. According to ESPN's Jason Sobel, both of Hammer's parents are avid golfers, with multiple championships at their local country club, and Hammer himself has been golfing since he was two years old.
According to Helen Ross of PGATour.com, upon arriving at Chambers Bay, Hammer played 36 holes over the weekend, including nine with his idol, Jordan Spieth. Like Spieth, the Masters champion and one-time prodigy, Hammer is already committed to University of Texas.
Spieth recognized Hammer's talent and how vital the experience could be for him:
"He's getting better experience than I had at his age. He maybe didn't expect himself to be out here testing his game this soon, but it just shows how the game is growing, how much better it's getting at a young age, and Cole's the living image of it. And I'm interested to see how he does this week. I think with really no expectations, it could help him. And on a golf course like this, you just never know."
Pat Wilson, a 24-year-old golfer who shot +9 on the day, raved about Hammer's composure to ESPN's Ian O'Connor:
"I can't even imagine what I'd be doing at age 15 on a stage like this. I definitely wouldn't be able to hold it together like he did... I was nervous as hell on those first few holes, and Cole's composure was amazing. To hit it that far and straight at 15 is something, but I was really blown away by his maturity. I was like, 'Wow, this kid is really good.'"
As Spieth mentioned, the pressure is essentially off for Hammer - anything positive he does will be a surprise and any of his struggles will be considered learning experience. At the very least, finishing above Tiger Woods at his first PGA tournament would be a noteworthy accomplishment.