Watch: Shane Lowry cracks up after getting penalty for rules violation at US Open

Shane Lowry left his playing partners in stitches during the second round of the US Open after he endured an embarrassing rules blunder.

Lowry came into the third men's major of the year at Oakmont feeling confident he could contend for the title given his recent form. 

But a nightmare first round of 79 saw the former champion golfer of the year left with a monumental task to make the 36-hole cut. 

By the time Lowry reached the 14th hole on Saturday afternoon he was already six-over par for the day and 14-over for the championship. 

Lowry's tee shot just missed the fairway and from there he could only find more rough just short of the green. 

He hacked out and his golf ball came to rest approximately 55 feet from the cup on the green. Then Lowry picked up his ball. 

The only problem was he forgot to mark it and a perplexed Lowry just stared at his caddie Darren Reynolds for a brief moment. 

Then the laughter followed from Lowry and his playing partners Rory McIlroy and Justin Rose.

Unfortunately for Lowry, the mistake saw the 38-year-old incur a one-shot penalty. 

Take a look at the moment here:

What do the rules of golf say?

This is all covered in Rule 14.1a. 

It states: "Before lifting a ball under a Rule requiring the ball to be replaced on its original spot, the player must mark the spot which means to: 'Place a ball-marker right behind or right next to the ball', or 'Hold a club on the ground right behind or right next to the ball'.

"If the spot is marked with a ball-marker after replacing the ball, the player must remove the ball-marker before making a stroke.

"If the player lifts the ball without marking its spot, marks its spot in a wrong way or makes a stroke with a ball-marker left in place, the player gets one penalty stroke."