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Kevin Na watched his first shot on No. 9 veer badly off course. His next stroke wasn't any better. Or the next one. Or the 11 after that.

Or maybe it was 12. Thirteen? Na himself couldn't keep track.

"I got done with the hole and I said (to my caddie), 'I think I made somewhere between a 10 and a 15," Na said. "But I think it's close to a 15."

Try 16.

J.J. Henry and former British Open champion Stewart Cink shot 5-under 67s to begin the Texas Open atop the leaderboard, but the spotlight belonged to Na, whose meltdown on the par-4 ninth ranked among the most dreadful in PGA Tour history and sunk his chances after an otherwise impressive first round Thursday.

Adam Scott, riding the momentum of his runner-up finish at the Masters, began his defense of last year's Texas Open championship strong and was a stroke back. The Australian shot a 68 and was tied with Charley Hoffman, Jhonattan Vegas, Vaughn Taylor and Kevin Chappell.

If it wasn't for No. 9, Na might've been right there with them.

Na birdied No. 18 to go 4 under on the other 17 holes. But so dreadful was No. 9 that the score was adjusted three times — first a 14, then 15, and finally, following a lengthy review of a video replay before signing his scorecard, it changed yet again to a 16.

He wound up signing an 8-over 80.

The worst single-hole score at a PGA Tour event belongs to John Daly, who had an 18 on the par-5 sixth hole at Bay Hill in 1998. Ray Ainsley took 19 shots on the par-4 16th hole at Cherry Hills in the 1938 U.S. Open.

Scott and Geoff Ogilvy, who finished the round two strokes back at 3 under, were in the group behind Na. They watched and waited to tee off as the 27-year-old hacked, whiffed and bumbled his way through a nearly 20-minute ordeal.

"There's some rocks in there and some pretty nasty stuff," Ogilvy said of the 474-yard ninth. "You don't have to do a whole lot wrong to have three or four attempts to try and get it out. It becomes a comedy of errors sometimes."

Even Na was smiling by the time he tapped in a 6-footer on the green.

"It's all a blur," Na said.

Here's what he does remember: his tee shot that sailed into the woods, where Na eventually found the ball. He called it unplayable and teed off again, but not with better results. Along the way he whiffed one stroke, ricocheted another off his inner thigh, tried two shots left-handed and watched the ball barely sputter forward on another stroke.

All while still in the woods.

"One bad hole can basically shoot you out of the tournament," Na said. "That's what I just did."

Having a far better day was Cink, who didn't decide to play at the Texas Open until he missed the cut at the Masters. He signed up 2½ hours after the deadline.

The 2009 British Open winner was glad he did, shooting a bogey-free first round.

"I didn't really feel like I would go forward by taking another week off," Cink said. "So I decided to add this one and just, you know, get right back to it instead of missing the cut at a major for another week."