Damien McGrane had a nightmare TEN on the 17th to crash to his second 76 on the trot.
The 536-yard par five claimed yet another Irish victim when the Kells man put three balls in the pond fronting the green to slither to the back of the field on 10 over.
Two years ago, Darren Clarke ran up an 11 on the controversial hole while in the 2000 American Express Championship Tiger Woods took an eight there on his way to victory.
McGrane said: “I hit my second shot into the water, dropped back and then spun two more balls back down into the water. That was three balls into the water and it added up to a ten.”
The Knightsbrook professional had three birdies in the first four holes to get back to two over par in just his second Valderrama appearance.
He slipped back to level for the day with two to play as wind and rain lashed the course and was bitterly disappointed to throw it all away at the 17th.
He added: “I had a chance of making birdie on 17 and walked off six shots worse than I was hoping for. But that’s golf. There’s always another day.”
It was also a disappointing day for defending champion Paul McGinley as he three putted the last for a one over par 72 that left him seven shots off the lead in share of 25th place.
Lashing rain forced him to remove his visor as he shaped up to a three footer for par after he had reached the green with two magnificent blows.
McGinley groaned: “The rain was dripping down from my visor and then it was dripping down from my head then when I took it off.
“I hit two lovely shots into the last and I was surprised to come up so short because my six-iron was right down the pin.
“The hole was cut just over a hump and I left the putt two or three feet short and missed it for par.
“That just seems to be the way for me this week. Nothing seems to be rolling for me but I am still there or thereabouts.
“I am not out of it year at seven shots behind but I still need something to happen. I need to hole some putts or chip in - something like that.
“I don’t mind the wind, it can blow all it wants, but when its rainy and windy it is much tougher.
“It started raining on my fifth hole and that was it then for the day. I am absolutely soaked now.”
As for Harrington’s chances of lifting the Order of Merit for the first time, McGinley believes his Ryder Cup team mate can do the business.
He said: “He’s got a great chance. He is doing exactly what he needs to be doing. He is right there in contention. Maybe this is the year for him to finally win the Order of Merit.”