It didn't because his main competition, Dustin Johnson, had just as much trouble keeping his ball in play down the stretch.
Johnson was within one stroke of his close friend after a birdie on No. 15, a hole he birdied all four rounds. The 3 he shot added significant tension to what had looked like a runaway win by Koepka - until Koepka's seven-shot lead and the way he was mastering the course disappeared in a flurry of bogeys on the back nine after a birdie at No. 10.
Two of the longest and strongest players on the PGA Tour struggled mightily with the swirling winds that at times reached 20 mph in some spots.
"I knew today, starting off, that it was going to play tough," said Johnson, who wound up two shots behind Koepka and will relinquish the No. 1 ranking to the winner. "You know, the wind was up. It was the most wind we've had all week."
The gusts might have been at their worst on the 16th hole, where Koepka pretty much clinched his second straight PGA, his fourth major, and became the first player to hold two back-to-back major crowns at the same time.
Johnson was having what had been by far the best round of the day. He was at 8 under overall when his tee shot on 16 landed smack in the middle of the fairway. But from 194 yards, his 5-iron approach caught a gust and soared over the green into nasty rough.
A nice chip out of that toward a flag whipping in the wind got Johnson to 7 feet, but he missed the putt.
"You know, wind was howling in my face a little bit off the right," he said. "I hit a 5-iron but almost went back and got a 4-iron because I didn't think the 5 was going to even come close, based on the shots that I've hit earlier in the round into the wind. The wind was just really eating the ball up when you're hitting into it.
"So I tried to hit kind of like just a little low draw. Hit the shot I wanted to right at the flag. Just I don't know how it flew 200 yards into the wind like that."
His momentum was gone with the wind, and he also bogeyed the 17th after a tee shot well right into the rough beside the par-3 green. The wind again played a role.
Koepka, who was on the 15th fairway and knew from the crowd's reaction that Johnson had dropped a shot, came to 16 having bogeyed four in a row, looking a bit worn and, perhaps for the first time in four days, sensing this was no cinch. He desperately needed to hit the fairway - something he did only six times all day - and did so. From 163 yards he put his ball 49 feet from the hole, providing more of a test. Koepka passed it by two-putting.
"Probably doesn't sound like much, but the putt on 16 I thought just gave me a little bit more confidence coming down the stretch," Koepka said. "I know I missed one on 17, but you know, I think 16 helped me make 18."
That was enough for the 29-year-old Koepka to hold on, denying Johnson a massive comeback for his second major title.
"With this golf course and this amount of wind, it's very, very difficult," Johnson said. "So I mean, it's definitely one of the tougher days we've played in.
"Obviously I knew starting seven back that it was going to be a big feat to catch Brooks. You know, I definitely gave him a run, though, so I was happy with that."
In the end, Koepka was the happiest, even if he hadn't exactly conquered Bethpage Black - or the swirling wind - on Sunday.
"I mean, I challenge anybody to go play this golf course in 15- to 20 mile-an-hour winds and see what they shoot," he said.
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