PINEHURST, N.C. -- A rules violation on the 18th hole Friday cost Hunter Mahan a chance to play into the weekend at the U.S. Open.
In the 18th fairway -- his ninth hole of the day -- Mahan hit Jamie Donaldson's ball toward the green. Donaldson didn't notice the mistake when he played his second shot, thereby hitting Mahan's ball.
Both players realized the mistake on the green, meaning they had to go back to the fairway and play their second shots again from their original spots -- each incurring a two-stroke penalty. Mahan went on to miss the 5-over cut by one stroke.
Both Mahan and Donaldson were using a Titleist ProV1, and players typically make another mark on the ball to help distinguish it if something like what happened Friday occurs.
Mahan was at a loss to explain what happened.
"I just hit the wrong ball," he said. "I don't know, it was one of those things. Off the tee it looked like that's where my ball should have been, and I couldn't explain to you how it ended up where it did. Just got to pay more attention."
Mahan's caddie, John Wood, took the blame.
"It was 100 percent on me. I was the first one to the ball," said Wood, who realized something was wrong when he set his bag down at the green. "And Jamie realized it first. And it started to sink in. You can't imagine yourself doing something colossally as stupid as that. But I did it. I won't forgive myself very soon after this."
Had they not fixed the mistake prior to hitting their tee shots at the next hole, both players would have been disqualified.
As it was, Donaldson's double-bogey 6 led to an 81, and he missed the cut.
Mahan, who finished with a double-bogey, shot 72 to finish at 6-over 146.
"It's probably going to cost us the cut," Wood said earlier Friday before the cut was final. "And he played so good today. The two-shot penalty probably cost him three because he had a really great look on the shot he hit in there for birdie. It's just one of those things you scratch your head at.
"I almost want to see the video of the shots to see what happened to them in the fairway. It's hard to believe ... again, it was my fault. It was my fault way more than anybody else in the group. Hunter's kicked right a little bit, Jamie' right on the left edge of the fairway. And they both have kind of a similar slash on the number.
"I assumed, wrongly obviously, that our ball was this one. And I walked up to it and I didn't give it a good enough look. I saw the slash and assumed it was ours. My mistake completely."
Other notable players to miss the cut Friday included Masters champion Bubba Watson, who finished at 6-over. Jason Dufner, Luke Donald and Charl Schwartzel also dropped out after finishing at 6-over. Dufner has missed the cut in two straight majors after winning the PGA Championship.
The Associated Press contributed to this report.