Sir Winston upset the odds when holding off favourite Tacticus to win the Belmont Stakes by a length on Saturday.
On his Classic debut for trainer Mark Casse, the 10-1 winner was produced late by Joel Rosario, moving from the rail to the outside to overtake front-runner Joevia.
"He's an amazing little horse. If you had asked me to rate our two-year-olds last year he would have been 16th or 17th," said Casse.
"I'm very proud of him because he's kind of what our operation represents – we develop horses. I start every horse out thinking they are going to win the Kentucky Derby or the Oaks.
"I tell you what, they all better watch out going to a mile and a quarter because Sir Winston will come running, too. Sir Winston is a pretty serious horse, so don't count him out," Casse said.
While making his move, Sir Winston appeared to hamper Preakness Stakes winner and stablemate War Of Will, who was second favourite but faded and finished ninth of the ten runners.
"You didn't see the real War Of Will," Casse added. "We've got to get him back and figure out what happened. We'll probably give him a little break and then aim him at the Travers."
The race caps a wild Triple Crown season that started with the disqualification of Maximum Security in the Kentucky Derby. He was the first horse in the race's history to be demoted after passing the post in front. Country House was awarded the contest at Churchill Downs.
There was drama in the second leg too when John Velazquez was thrown from Bodexpress coming out the stalls in the Preakness Stakes at Pimlico.