Now he's a household name, despite playing in Denver's read-option offense, where wide receivers serve more as blockers and decoys than pass-catchers.
Thomas ended the quickest overtime in NFL history - 11 seconds - with the longest winning touchdown in any playoff game ever. His electrifying 80-yard catch Sunday from Tim Tebow sent the Broncos to a 29-23 win over Pittsburgh.
Dogged by a broken foot, sprained ankle, concussion, torn Achilles and fractured finger since turning pro, Thomas said Monday he never doubted he'd regain his health and prove he was a worthy first-rounder.
"It was just the freak accidents that were just happening," Thomas said. "I knew once I got back on the field and got healthy, I can make some plays and help my team."
Thomas had a rough rookie year after leaving Georgia Tech following his junior season. In training camp, he aggravated a surgically repaired left foot that he had broken in pre-draft workouts, then sustained a concussion and high ankle sprain during the season and only played sparingly.
Then in February, Thomas was doing lateral footwork and conditioning drills at his alma mater when he felt pain in his right heel. Surgeons had to repair his torn Achilles tendon, and they told him he might miss the entire 2011 season.
"I didn't know it was that serious because I walked off and I went home. I went to the doctor the next day. He told me it was ruptured," Thomas said. "He said it was like 8-12 months before I get back and I asked him, what's the fastest somebody's ever been back? And he was like, `Five months.'
"It maybe took me six months to get back to running."
Impressed by his speedy recovery, the Broncos elected to keep him on their 53-man roster when the season started rather than placing him on the PUP list. But in his first padded practice two days later, he got hurt again when cornerback Champ Bailey broke up a pass that struck Thomas square on his left pinkie.
"I thought it was a jammed finger, so I kept on practicing," said Thomas, who realized it was more serious when another ball hit him on his fractured finger.
Another round of rehab.
He really found his stride down the stretch.
Since Dec. 1, the burly receiver who packs 230 pounds on his 6-foot-3 frame has been one of the most dominating players in football.
His 29 catches for 652 yards - a league-best 22.5 yards per catch - four touchdowns and 108.7-yard receiving average are second only to Detroit's Calvin "Megatron" Johnson.
For much of the season, he was frustrated playing in an offense that affords wide receivers few chances to strut their stuff.
"It's been tough," Thomas said. "We don't pass the ball a lot, as you know."
Thomas should be used to it; he played in Paul Johnson's triple-option offense at Georgia Tech, a system that was considered ill-suited for the NFL until the Broncos brought back the read-option at midseason following Tebow's promotion.
"We did pass it more in college," Thomas said. "It's frustrating, but once you're winning, when we went through the little six-game winning streak, it's fine. Once you're losing, it bothers you a little. I feel like what helped me out is just being patient and taking advantage of the chances I got."
His teammates were jubilant over the Broncos' first playoff win in six seasons but were especially glad for Thomas.
"He's been through a lot in his short career," Eddie Royal said. "I'm just happy for the guy because I know the hard work he puts in."
Royal said the Broncos see Thomas shine every day "making amazing catches and running past people" in practice. "But that game showed what he can do game in and game out."
The play-action fake worked to perfection because the Broncos had run on 21 of their 22 first downs to that point, and all 11 defenders were within 4 yards of the line of scrimmage when the ball was snapped.
"I knew walking up to the line and I saw the safety come down, I was like, `This is going to be a big play,"' Thomas said. "The middle of the field was wide open and all I had to do was beat the corner. And once I beat him, it was like, nothing but green grass. And I knew I was going to score."
Thomas' 58-yarder might have gone for a 73-yard score had he kept racing across the field in similar fashion but Taylor caught him when he slowed to cut back.
"I tried cutting it back to the sideline and Coach was like, `Use your speed,"' Thomas recounted.
So, in overtime he never slowed down, running right through the end zone and up the tunnel while Sports Authority Field shook.
Thomas, however, was confused about the playoff overtime rules that allow both teams to get the ball unless one of them scores a touchdown first. He also was thinking back to college, where both teams get the ball in overtime.
"I thought the defense had to go on the field," Thomas said. "I actually didn't know. I saw Champ run up the tunnel with me. I was like, `What's going on?' And then I looked out, I saw everybody on the field, so I assumed the game was over with."
That's when he realized he had produced one of the greatest playoff endings in NFL history, finishing with a career-high 204 yards on just four receptions.
It was the shortest overtime ever and the longest touchdown ever to win a playoff game.
Carolina's Steve Smith set the previous record for the longest overtime TD, a 69-yarder from Jake Delhomme to beat St. Louis 29-23 on the first play of the second overtime on Jan. 10, 2004.
"This was a big play and that's the one I was focused on," Fox said with a smile.
Notes: Fox said WR Eric Decker's left knee injury was "just a sprain, so he'll be day-to-day, so that was actually good news." ... Tebow's 31.6-yard average per completion Sunday was the second-best ever by a QB with at least 10 completions, topped only by Joe Namath's 33.1 average for the Jets against Baltimore on Sept. 24, 1972.
Follow AP Pro Football Writer Arnie Melendrez Stapleton on Twitter: http://twitter.com/arniestapleton