The 28-year-old rookie was taken to hospital on Friday after suffering an elevated heart-rate and shortness of breath, but returned to Lake Buena Vista to shoot a one-under 71 and hold a two-stroke lead going into the final round.
"I honestly didn't think I was going to get through it. I just stayed strong,” Beljan said.
Beljan's stirring third round left him with a 13-under total of 203, two strokes clear of fellow Americans Brian Gay and Josh Teater, and South Korea's Charlie Wi.
Beljan was again plagued by Friday's symptoms, but said peanut butter sandwiches helped calmed him down.
"On about (holes) eight and nine I told my caddy, 'Look I am not feeling good, I am starting to get the same type of symptoms,'" said Beljan, who is fighting for a spot on the US PGA Tour for 2013.
"So we ate a couple of peanut butter sandwiches and we tried to breathe a little bit. Then the birdies on 10 and 11 kind of helped slow it down."
Beljan made four birdies for the round after stumbling with bogeys on the first and third holes.
"I was extremely nervous and scared this morning showing up here in front of everybody not knowing how I was going to be able to handle things. But to get through today was a big stepping stone,” he said.
"It was nice to be able to walk around and to be able smile. Yesterday (I) was hanging on for my life."
He is hoping for an even brighter Sunday, even with 10 golfers within three strokes of his lead.
"I am looking forward to a nice night's sleep ... sleeping with my shoes off in a bed and having an opportunity of a lifetime tomorrow," he said.
Doctors were not sure he should have spent the day playing golf.
"They released me saying that they thought I was good enough maybe not to go play golf, but at least to leave the hospital," said Beljan, who left the course in an ambulance on Friday.
"But shoot, the position I'm in, it's kind of hard not to show up."
Beljan shot a sparkling 64 on Friday to take a three-stroke lead despite suffering breathing problems and having to lie down on the course several times during his round.
He only had an hour's sleep at hospital, and that was with his golf shoes on, he added.
Beljan said he had suffered similar episodes in the past but not as bad as Friday's ordeal. He passed out on a flight from Reno, Nevada, last month and had to be taken to the hospital once the plane landed. Doctors were unable to come up with a diagnosis, he said.