PINEHURST, N.C. - Well, this was awkward. Somehow playing partners Jamie Donaldson and Hunter Mahan hit each other's golf balls.

The scene: the 18th green, the ninth hole of the day for Donaldson and Mahan. While on the green, they realized they'd hit the wrong ball on approach, and had to trudge back down the fairway to do it all over again.

How does something like this happen? Mahan's caddy Johnny Wood fell on the sword afterward, saying it was "my fault" over and over again in talking with reporters after the round.

"I assumed, wrongly, obviously, that our ball was this one," he said. "And I walked up to it and I didn't give it a good enough look. I saw the slash [marking on the ball] and assumed it was ours. My mistake completely."

"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," Mahan said. "Just got to pay more attention."

Mahan and Donaldson both play Titleists, and according to Wood, both balls had the similar slashes marked on them. Here, let's let Hunter himself tell you how he does it:

Anyway, the penalty was +2 to for both players, but if they'd played the entire hole with the wrong balls, they would have been disqualified. Donaldson was already in the midst of a free-fall; he followed Thursday's even-par round with a nightmarish 81.

Mahan, meanwhile, finished at even par to stand at +2 on the day, just below the projected cut line. In other words, the mistake very well could have cost Mahan a spot on the weekend.

As for the question of whether the players themselves bore some responsibility, well, Wood took that on himself too: "It's a rhythm you get into as a group," Wood said. "And if I'm the first one there, I go to a ball, I get a yardage ... But there's no reason for Hunter to think that I went to the wrong ball or Jamie or Mick [Donaghy, Donaldson's caddy] to think that I went to the wrong ball." [Wood also indicated that he doesn't expect there to be any recrimination from this: "Hunter knows how bad I feel," he said. "He's a great guy to work for. I don't think there will be anything else to come from this."]

"It's one of those fluke things," Mahan said. "I've played a lot of rounds of golf now and it's happened maybe one time before."

"You can't imagine yourself doing something colossally as stupid as that, but I did it," Wood said. "I won't forgive myself very soon after this."

Going forward, expect these guys to tag their golf balls like old-school NYC subway cars from now on.

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Jay Busbee is a writer for Yahoo Sports. Have a tip? Email him at jay.busbee@yahoo.com or follow him on Twitter.

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