Incheon - Confusion and controversy struck the Presidents Cup on Friday when Phil Mickelson and Zach Johnson lost the seventh hole "twice" after being penalised in a baffling rules infringement.
The US pair stood on the seventh tee at the Jack Nicklaus Golf Club, Incheon, all square in their four-ball match against Aussie duo Adam Scott and Jason Day.
But by the time they walked off the green they were two holes down - something that would seem impossible in match play golf.
It turned out Mickelson had breached a rule which states you must play the entire round with the same brand and model of golf ball.
Mickelson noticed he had a different model of Callaway ball after hitting his tee shot on the seventh and reported himself to the match referee, who prevented him from finishing the hole.
Johnson made a par, but Day won the hole for the International team with a birdie three.
Rules expert Steve Rintoul explained on the Golf Channel that the breach of the one-ball rule provides for a "match adjustment" loss of one hole - in effect the Americans lost the hole twice.
The ruling had competitors, watching media and spectators alike scratching their heads. Golf fans and even professionals were quick to take to social media to criticise the rules.
Former US team member Keegan Bradley said on Twitter:"How can you lose a hole twice???! #ussgarules #wow"
One Twitter user, Ari Marcus, said: "So apparently you can lose a hole twice now... How can any match be closed out early now? I.E. How can you lose 2&1 if this is possible?"
Another, Matt Blackly, tweeted:"Yet again the rules of golf are as clear as mud and destined to turn people away from the game! #Simplify it."