Sir Winston, ridden by Joel Rosario, won the Belmont Stakes, the third contest in US horse racing’s Triple Crown.
The win gave trainer Mark Casse a second Triple Crown win this season.
Race favorite Tacitus was second and Joevia was third in Saturday’s contest.
The winning time for the 1 1/2-mile race was 2:28.30, four seconds off the record set by Secretariat in 1973.
“He’s a very nice horse. You have to let him do his thing,” Rosario told race broadcaster NBC. “I just took my time with him.”
Rosario also rode Tonalist to a Belmont win in 2014.
Sir Winston spent much of the race near the back of the 10-horse field but began to move up with six furlongs to go. Rosario guided his chestnut colt through an opening next to the rail.
But when the field hit the homestretch, Sir Winston moved out several paths, in front of Preakness Stakes winner War of Will, then romped to a one-length win.
Casse, who also trains War of Will, said the horse looked like he was struggling.
“Normally, he’s on the bit and wanting to go, and I thought maybe around the half-mile pole, five-eighths pole, I thought he was struggling a little,” he said at a news conference.
He said Sir Winston, a 10-1 betting favorite, is an “amazing horse.”
If at this time last year, if you had asked me to rate our top 20 2-year-olds, he would have been about 16th or 17th,” Casse said. “But I’m very proud of him because he’s kind of what our operation represents, and that is … I feel like we develop horses.”
Kentucky Derby winner Country House was not in the race. War of Will faded to ninth place.
It was the 151st running of the race at Belmont Park in Elmont, New York.
CNN’s Kevin Dotson contributed to this report.