Crunching the numbers after the first round of the U.S. Open:
• How tough was Erin Hills? The top six players in the Official World Golf Ranking - Dustin Johnson, Rory McIlroy, Jason Day, Hideki Matsuyama, Jordan Spieth and Henrik Stenson - were a combined 21 over par.
• Johnson's 75 was his highest score in his last 14 U.S. Open rounds played. He had been inside the top six after each of his previous 12 U.S. Open rounds.
• Perhaps DJ's struggles shouldn't have been a surprise; this is the sixth straight year in which the defending U.S. Open champion opened over par.
• Spieth shot 1-over 73, marking the fifth straight major in which he has opened with par or worse. In his last five majors he is a combined 6 over in the first round. In the first rounds of his five previous majors he was 22 under.
• Spieth needed 32 putts - just one off his most in the first round of a major.
• Speaking of one off, McIlroy's 78 was just one shot off the worst opening round of his major career. It's the seventh opening round of 74 or worse in a major - and he missed the cut the previous six times.
• Day's 79 was his worst opening round in a major by three strokes, and one shot off his worst career round in any major (80, 2012 PGA, second round).
• Rickie Fowler's 7-under 65 tied the lowest first-round score in relation to par in U.S. Open history. The other two instances both came in 1980, when Jack Nicklaus and Tom Weiskopf shot 7-under 63s in the first round at Baltusrol.
• Fowler is only the third player to begin a U.S. Open with a bogey-free 65 or better, joining Tiger Woods in 2000 and McIlroy in 2011. A good omen for Fowler: Those two went on to win by a combined total of 23 strokes.
• Did Fowler's 65 seemingly come out of nowhere? In his five previous U.S. Open rounds he was 27 over par. Thursday's 65 is his lowest career round in a major.
• What was the difference? He hit 16 of 18 greens in regulation Thursday. In those five previous Open rounds, his GIR percentage was 56.7.
• Another player having a career day Thursday was Paul Casey, whose 66 was his lowest career score to par in a major round.
• Casey's presence on the leaderboard shouldn't come as a surprise, though. He is the only player who finished in the top 10 in each of the previous two majors. He was T-10 at the PGA Championship and sixth at the Masters.
• Casey's best finish in a major is T-3 at The Open in 2010 at St. Andrews.
• Tied with Casey for second is Xander Schauffele, the 23-year-old former Long Beach State and San Diego State player. He became the only player in the last 30 years to shoot a bogey-free 66 or better in his U.S. Open debut.
(Information compiled by the Golf Channel Research Dept.)