The event's defending champion had no bogeys and seven birdies in the round to get to seven strokes under par to begin the tournament. No one else in the morning session was better than three-under.
Koepka was especially impressive with his putter during the round, sinking several long opportunities for birdie:
Per PGATour.com, he gained 3.273 strokes in the round on the green alone.
Even though Bethpage Black is proving to be as difficult a course as it was at the 2002 and 2009 U.S. Open tournaments, Koepka has made it look easy.
His performance continues an outstanding run both at the PGA Championship and majors overall:
The 29-year-old has already won three major titles—the 2018 PGA Championship, 2018 U.S. Open and 2017 U.S. Open—and finished tied for second at the Masters this season.
He also recently said his goal is to get to "double digits" in major wins, per Ben Everill of PGATour.com.
While this would put Koepka among the best all time, he is certainly on his way considering how well he has played.