Rory McIlroy earned plaudits for his integrity as he suffered a frustrating second round in the US PGA Championship in San Francisco, while Shane Lowry's frustration led to him snapping a a club over his knee at Harding Park. 

McIlroy recovered from a slow start at Harding Park to birdie four holes in a row from the seventh and get within five shots of the lead, only to run up a triple-bogey on the 12th after three-putting from seven feet.

A birdie on the 16th repaired some of the damage and the four-time major winner eventually signed for a 69 to finish one under par, seven behind halfway leader Li Haotong.

The incident which saw McIlroy widely praised on social media and during the television commentary had occurred on the third hole, when a TV reporter accidentally stepped on his ball in the rough.

McIlroy was entitled to replace the ball under the supervision of a rules official but refused to accept what he thought was a favourable initial lie.

"I just wouldn't have felt comfortable," McIlroy said.

"The rule is try to replicate the (original) lie. No one really knew what the lie was, but if everyone is going around looking for it, it obviously wasn't too good.

"So I placed it and I was like, that just doesn’t look right to me. So I just placed it down a little bit.

"At the end of the day, golf is a game of integrity and I never try to get away with anything out there. I’d rather be on the wrong end of the rules rather than on the right end because as golfers, that’s just what we believe.

"I would have felt pretty wrong if I had taken a lie that was maybe a little better than what it was previously."

Lowry lies just one shot behind the Holywood golfer after a round of 72. 

The Offaly man started the day brightly, with birdies on the first and fifth holes, but three consecutive bogeys from the eighth hole and another on 12 led the Open champion to a fit of pique that saw him snap his club in two after his second shot on the unlucky-for-some 13th, where he registered yet another bogey. 

A birdie on the 15th is unlikely to have done much to quell his frustration with the round.