Sir Barton was still a maiden as of his entry into the Kentucky Derby at Churchill Downs, in Louisville, Kentucky. He was a new-comer with no real expectations resting on his performance. He was entered into the Derby as a "rabbit" for his stable-mate, Billy-Kelly, who had a higher profile, and greater expectation of winning the Derby. A "rabbit" was a horse who was placed in the race to speed ahead early in the race, to pull the pack fast early, tiring the horses, and setting the race up for the other horse. Apparently Sir Barton was not in on the deal, and handily won the derby by five lengths.
Four days later, on May 14, Sir Barton ran in the Preakness Stakes, at Pimlico Race Course, in Baltimore, Maryland. (Trivia: The Preakness was run at Morris Park Racecourse in the Bronx, NY in 1890, and from 1894 to 1908, Gravesend Race Track at Coney Island, hosted the Preakness.) Sir Barton again won the race.
With barely any rest, ten days later, Sir Barton was at Belmont Park, winning the one-mile Withers Stakes.
Finally, Sir Barton was given a rest, but only until June 11, for the Belmont Stakes. Sir Barton was in a field of only three horses, and ran the mile and three-eighths in a record breaking 2 minutes: 17 2/5 seconds.
These four wins were accomplished in a mere 32 days, and in doing so first accomplished a feat that has only been repeated 10 more times in the ensuing 93 years, and has not been done since 1978, when Affirmed won the Triple Crown.