The then-21-year-old Texan took the golfing world by storm last year when he won the Masters and US Open and came close to becoming just the second player ever, after Ben Hogan, to win the first three majors of the year at the British Open.
He finished the year with a 1-1-T4-2 record in golf's four crown jewels tournaments -- a performance that only Tiger Woods in recent years has been able to match.
Asked if the Grand Slam was achievable, Spieth replied: "You know what, I would have said prior to last year, no.
"And it's very, almost, conceited for me to say because of last year maybe. But we were so close and it was one break here or there.
"Now we got the breaks this week, and we certainly got the breaks at the US Open. It was a golf course where you needed to get breaks at Chambers Bay. Here you have kind of got to create your own.
"There might be someone some day that comes along that's as dominant as Tiger was in 2000, 2001 and, yeah, if they're just that good, you can get the breaks, and even if you don't, you can still maybe win.
"Man, I got as good breaks as I could last year and didn't pull it off. But we were very close."
"I think it can happen, but especially with the way
- Stunning achievement -
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Spieth's win at Augusta National last year was a stunning achievement as his 18-under total matched the best ever, set by Tiger Woods, and he became the second-youngest Masters winner after Woods.
And although the Texan will start his defense without a tournament win since the start of the year, he feels like his game is coming together nicely.
"We know we're capable of playing this place. We have proven it to ourselves the last two years. So the focus is on this week, and we feel as confident as probably ever.
"So the game actually feels better right now than I think it did last year on Tuesday, so that's good if we can keep it consistent."
Spieth has a comfortable mid-morning start in Thursday's third round in the company of England's Paul Casey and fellow 22-year-old Bryson DeChambeau, a US amateur.
