PORTRUSH, Northern Ireland — A lot of golfers struggled at Royal Portrush on Thursday, but no one had a day as lousy as David Duval.

Duval, a past champion who won the 2001 British Open, shot a 20-over-par 91 that included a 14 on the par-5 seventh hole, on which he hit the wrong ball and had to start the hole over.

"Very unique, awful situation," concluded Duval, who had the poise to stick around and talk to reporters after the worst round of his career.

"I've posted 85 twice, but never a 90," he said. "It was a long day, rough day."

Oddly, he got off to a terrific start, with birdies on the first two holes. He parred the third and fourth, but then took an eight on the par-4 fifth when he lost a couple of golf balls.

Two holes later, disaster. He lost his first tee shot on No. 7, and his provisional landed in the rough. A marshal said he found the ball, but neither he nor Duval checked it closely enough. It wasn't Duval's ball.

"I asked if it was a 2, a Titleist 2," Duval said. "And then I looked at it and saw 2 and then played almost the entirety of the hole, and it turns out with the wrong ball. So then I had to go back to the tee, basically start the hole over."

Duval blamed himself for the error, failing to check whether the 2 on the ball was black or red.

"I'm at fault," he said. "I didn't take a close enough — it happened to me once before where a marshal is standing right next to the ball, kind of glanced down. I usually use a yellow mark, it's hard to see. And I don't see red very well. And so standing looking down at it it's a 2. So just my mistake."

Duval's score originally was listed as a 15, but then was reduced by two strokes because of a calculation error. Officials later determined it was a 14.

That represents the highest score on a hole at the British Open since at least 1983, when the PGA Tour began keeping hole-by-hole records. The previous high score of 11 was made by four different players, most recently Henrik Stenson in 2011.

Duval, who pulled out of the Open on the second day last year, said he intends to play Friday, and explained his thinking about posting his score rather than withdrawing.

"You have an obligation as a professional athlete, if you play, you post your score," he said. "So, well, am I happy about that? Is there some, I don't know, embarrassment about that? I don't know. But I teed off in the Open and I shot a (91) today, so I put it on the board."