Trainer Michael Matz insisted Union Rags had always possessed star quality after the colt claimed the Belmont Stakes.
Although the race was greatly diminished by the withdrawal of Triple Crown aspirant I'll Have Another, New York racegoers were still treated to a blockbuster finish.
Union Rags, ridden by John Velazquez, came fast and late in the US$1million heat to deny Paynter by a short neck.
Matz said: "We always thought this horse had Triple Crown potential.
"When we trained him, we gave him four races as two-year-old and gave him a rest and had a good plan.
"He never missed a beat. His first race (this year) couldn't have been any easier. He had trouble in his second race and his third race.
"I do really think that this horse, when he has a clean trip and can show himself, is one of the best three-year-olds in this crop.
"Whether he could have done something against I'll Have Another, I don't know, but it sure would have been fun to see."