No. 10 in the world and consistently on the short list of potential contenders in the big ones, Casey last threatened to win a major all the way back at the 2004 Masters Tournament.
"It's gone very quickly, I must admit," said the affable Englishman of the six lean years since.
After tying for the low round of the day Saturday with a 67, Casey is the only guy within seven strokes of cruising leader Louis Oosthuizen at the British Open, sitting four back at 11-under par. He is in the best position to rewrite his personal history before he celebrates his 33rd birthday on Wednesday.
"I would love to replicate that (Sunday)," said Casey of his bogey-free 5-under round. "I'm not sure it would be enough with the way Louis is playing."
It might at least be enough to boost Casey's major confidence as he approaches his "peak" years. He seemed to be hitting that peak in 2009 after finishing runner-up in the WGC Match Play and winning his first PGA Tour event at the Houston Open.
But at last year's British Open at Turnberry, Casey pulled a rib muscle that pretty much scuttled the rest of his season. He didn't play in another PGA Tour event all year. The first four-round event he competed in was Tiger Wood's Chevron World Challenge in December.
"At that stage and even going into early this year, I was very unsure of how things were going to go, and sitting here right now I'm ecstatic," he said. "You know, even right now, occasionally I feel the muscles in the ribs. In no way do they affect my golf. But it's a small reminder that, you know, quite often you take for granted a lot of things."
When he first broke onto the major scene after a stellar collegiate career at Arizona State, it was easy to take Casey's talents for granted. His highest career major finish came in his first at-bat at Augusta National, when he entered the final round of the 2004 Masters one shot behind co-leaders Phil Mickelson and Chris DiMarco and shot 74 to tie for sixth.
"I've not played the golf I've wanted to to give myself those opportunities," he said of his major record since that includes a tie for seventh at the 2008 British and top 10s at the 2007 Masters and U.S. Open. "That's been a bit frustrating. But you know, I've worked very hard, and I feel that I've got 10 years or so to take advantage of my game. I can't tell you what's going to happen in the future, but I desperately want to be a major champion, and I think I have the ability. And I think I'm working hard enough, but that doesn't guarantee anything, as we know. So we will see."
That his best opportunity is coming in the British Open is a surprise even to Casey. Along with Luke Donald, he's arguably the most Americanized English golfer having gone to the U.S. to attend college and never leaving. He still lives in Arizona and is more accustomed to golf in the states than his homeland.
"I'll be the first to admit, I worked so hard when I got to the states at being able to play -- certainly when I went to college, changing my ball flight, getting a high ball flight, being able to play the style of golf courses over there -- that when I came back to play in the British Isles, I had kind of forgotten how to play a little bit," he said. "It's in there. I know how to do it, and I love doing it."
So attempting to become the first Englishman to win a major since Nick Faldo on the same course where Faldo triumphed in 1990 is a big moment for Casey.
"I'm not sure I'm able to explain what it would mean," he said. "It is the ultimate for me. Probably even more so because links golf is something I've struggled with. I've always felt my best opportunity has been somewhere like Augusta with my ball flight. And I've worked very hard to give myself the opportunity to compete in an Open Championship, and therefore the opportunity to win, as I've now got."
Casey's opportunity is thanks to some nearly flawless golf that has been quietly building. He finished runner-up again to countryman Ian Poulter at the WGC Match Play, but done little since.
Casey was in sixth place after two rounds of the U.S. Open last month at Pebble Beach, but wasn't swinging that well and had sort of "Band-aided" his game together, said his caddie Christian Donald -- Luke's brother who has been carrying for Casey for the last six months.
Casey finished 77-80 to place 40th at Pebble. There have been no such issues this week.
"He's just hitting it so straight," Donald said. "He's controlling his irons, everything. He's just not missing any shots."
Casey made a triple-bogey on his card on the Road Hole on Friday, but last scribbled a bogey on his card on the eighth hole of the first round. When that was pointed out to Donald, he scratched his head in awe at the stat.
"He's not doing anything wrong," Donald said. "It's been stress-free for me."
"I can't emphasize enough that I'm just having fun out here," he said.
Even that triple-bogey Friday morning didn't bother him.
"Other than hitting my tee shot too far left, I didn't hit a bad shot," he said.
That tee ball burrowed into the thickest rough on the course that is just past the landing zone of the 17th. His attempted pitch-out moved "about a half inch down, because it didn't move forward."
"But I moved enough grass on my first shot that I could get a club on it," he said with a laugh. "I was so scared that if I went after it hard with my wedge I'd be in room 312 of the hotel."
Casey's ability to bounce back without any more blemishes has been the secret to his success this week on a course he readily admits is not the most suitable to his game.
"You have to have a sense of humor to play links golf," he said of the inevitable pratfalls that will come.
Casey promises to do just that as he tries to reel in Oosthuizen and hold off any other chargers.
"I'm going to go out there with a smile on my face and enjoy it," he said.
If all goes well, he might just skip that whole top-five nonsense and go straight to the top.