There were more than a few folks who wondered if the Chinese prodigy who was about to play the Masters earlier this year would be able to withstand the rigors of Augusta National as a 14-year-old and break 80.
It is a big ballpark, after all, and for all of his amazing skills, the fact was, he was barely a teenager, in the equivalent of seventh grade, about to compete on golf's grandest stage.
Players with far more credentials have failed to break 80 over the years and, well, for Guan, it would hardly have been any shame had he posted a couple of scores above that number, thanked all for the invitation to the Masters, and headed back to China.
Of course, it didn't quite work out that way. Far from it.
Guan shot an opening-round 73 and despite a slow-play penalty during the second round made the 36-hole cut. He shot all four rounds in the 70s, finished 58th and was the low amateur.
Not bad for the youngest competitor in the history of the tournament.
And now the event where it all started is upon us.
Guan made his way into the 2013 Masters because of his victory at the 2012 Asia-Pacific Amateur Championship, the 2013 version of which begins Thursday.
"It has given me more confidence and I can now know how to blend practice and I think I've learned so much in all of this year," Guan said during a conference call.
He will attempt to defend his title at Nanshan International Golf Club in Longkou City, China.
Five years ago, Masters chairman Billy Payne unveiled his plan to tap into one of golf's growing markets, setting up a tournament for amateurs in the Asian region along with the help of the R&A.
A big carrot came with it: a spot in the Masters.
That immediately gave the Asia-Pacific Amateur Championship some cachet, and so far it is hard to envision it going any better.
Japan's Hideki Matsuyama won the tournament twice and made the cut at the Masters both times. He turned pro earlier this year, made the cut in three major championships and earned his PGA Tour card. Last year was highlighted by all the interest in Guan.
"It has gone really well, and better than any of us could have hoped," said Peter Dawson, the CEO of the R&A. "Matsuyama won it twice and the way he is making out as a professional has been terrific. The publicity surrounding Guan [is] big. The tournament is making a real name for itself.
"I think it is doing what was intended, which is to increase the profile of golf in that part of the world and inspire amateurs in that part of the world, as well."
Guan's victory last year was impressive enough. He defeated a field of players older and more experienced than himself. Then came his exploits at the Masters, where -- being a short hitter -- he was expected to struggle at massive Augusta National.
But he has an impeccable short game and had plenty of admirers, including two-time Masters champion Ben Crenshaw, who raved about Guan after playing two rounds with him at Augusta.
"When I went back to China, I think more people recognized me, appreciate their support a lot," Guan said. "I think the most important thing is that more and more people, and especially young Chinese people, know about golf and start to pick up the game.
"More people know more about the Masters and I think it means a lot to the young players in China and they think, probably, the Masters is not that far away from them."
Guan, who turns 15 on Friday, stuck around after the Masters and played in four PGA Tour events, making the cut in New Orleans but missing the cuts at the Byron Nelson, Memorial and Memphis tournaments.
He returned to China in August, and has been going to school while continuing to work on his game. His only tournament since was a Japanese tour event in which he missed the cut.
The goal this week, of course, is to win and make it back to the Masters.
"I don't feel much more pressure this time," Guan said. "But I think it is still the greatest amateur event in the world. So I really hope to win it again, and I feel like if I am playing and I'm having a really good week, I can win again."
If Guan fails to defend his title, there is still the chance that he could get a special invite from the Masters. The tournament can offer special exemptions to foreign-born players, and the 11 dating to 2002 have gone to Asian players, including three to Japan's Ryo Ishikawa. The last amateur to get a special invite was Australia's Aaron Baddeley in 2000.
So precedent exists, and given the popularity of the Guan story and his surprisingly impressive play, don't rule him out.
As for Guan's own future?
"I still have no idea about turning pro now," he said. "I'm working on my game now, still working on my game and schoolwork is very important for me still. So I think it is a still a long way to go.
"I hope I can still go back to Augusta next year. But other than that, I don't have a plan now."