A quadruple-bogey 8 at the first hole might not have been the most embarrassing part of Rory McIlroy's wild opening round at the British Open.

Three-putting from 4 feet for a double at the par-3 16th also left the Northern Irishman shaking his head, and another double at No. 18 saw him stumble home for an 8-over 79. It tied his worst first round at the British Open.

McIlroy was 12 strokes off the lead, his major drought almost certainly extending to a sixth year. He said that heightened expectations played no part in his poor play.

"I'm pretty sure anyone starting with a 79 in this golf tournament doesn't think about winning at this point," McIlroy said.

He admitted he was nervous on the first tee, where he went out of bounds, but not because he was playing a major in his home country for the first time. He added that missing a tap-in at the 16th was "inexcusable."

McIlroy went out of bounds on his first shot of the day, then left his ball unplayable in thick brush near the green and ended up with a quadruple-bogey 8.

McIlroy went out of bounds left in an internal area of the course off the tee. After hitting his provisional left again into the rough, his approach cleared a bunker but landed in a patch of thick grass and he was forced to drop. He chipped onto the green but missed a 6-foot putt.

It was later revealed that McIlroy's opening tee shot hit a woman out of bounds and broke a cellphone in her pocket. The R&A said a 34-year-old woman from Northern Ireland was standing along the side of the first fairway when she was hit by the errant shot.

The 2014 champion holds the course record at Royal Portrush, shooting a 61 when he was 16 in the North of Ireland Amateur.

Heading into this year's tournament, the first in Northern Ireland since Royal Portrush hosted the event in 1951, McIlroy was considered to be a strong contender for a second British Open title.

Despite his problems on one and 18, McIlroy won't be able to claim the worst single hole score of the day. That mark belongs to David Duval, who posted a 13 on the par-5 seventh hole.

Duval, the 2001 champion also had a quadruple-bogey 8 on the fifth at Royal Portrush. He birdied the first two holes and is 11 over through eight.

Duval won at Royal Lytham & St. Annes 18 years ago but now spends more time as a golf commentator than he does playing professional events.