ERIN, Wis. (AP) - A triple-bogey didn't stop Paul Casey from grabbing a share of the lead at the midway point of the U.S. Open at Erin Hills.

Casey sandwiched a pair of bogeys around his triple during a four-hole stretch of the back nine. Fortunately for the Englishman, he also carded five straight birdies on the front nine and signed for a 1-under 71 that leaves him at minus-7 through 36 holes.

Brian Harman, Brooks Koepka (KEHP'-kuh) and Tommy Fleetwood are part of the four-way tie after each fired a 2-under 70. Koepka had the outright lead with four holes left in his round before a bogey on the par-3 sixth hole.

First-round leader Rickie Fowler is one shot back and tied with Jamie Lovemark and J.B. Holmes. Fowler lost his lead with three straight bogeys on the back nine.

Amateur Cameron Champ is in the mix at minus-5 following a 3-under 69. The 22-year-old Champ is trying to become the first amateur since Johnny Goodman in 1933 to capture the title.

The course played much tougher than it did during Thursday's round. Players noticed firmer greens that were allowing putts to race past the hole.

Defending champion Dustin Johnson missed the cut, as did Rory McIrloy and Jason Day. It's the first time since the Official World Golf Ranking began in 1986 that the world's top three players missed the cut in a major.

Former Masters champion Danny Willett has withdrawn from the Open with a back injury. Willett shot a 9-over 81 in the first round and then withdrew before his tee time in the second round.