2004: Two-year-old season

Borrego's career as a racehorse began in October 2003. Being by the Irish sire El Prado, a sire known for producing both turf and dirt runners, trainer C. Beau Greely debuted his homebred colt on the turf in a one mile Maiden Special Weight at Santa Anita Park. After running 4th in his debut, he won for the first time in his next start, and went on to win once more in his juvenile season.

2005: Three-year-old season

Greely started Borrego on the road to the Kentucky Derby in 2004, first in the Sham Stakes at Santa Anita Park.

He earned his spot in the Derby after respectable finishes in the Louisiana Derby and Arkansas Derby, but could do no better than 10th on Derby Day. He wheeled back two weeks later in the second leg of the Triple Crown, Pimlico's Preakness Stakes. He ran 7th in that race, but rebounded that fall to finish 2nd in a pair of stakes races.

2006: Four-year-old season

Borrego came back for his four-year-old season, and after several solid efforts he finally broke through in the Pacific Classic at Del Mar, rallying from well back to pull off a 1/2-length upset at 11/1 odds.

Greely shipped Borrego across the country for the Grade 1 Jockey Club Gold Cup at Belmont Park. Under regular rider Garrett Gomez, dropped back to his usual position near the rear of the pack early before unleashing a rally en route to an effortless 4½ length win. With that victory he became the first horse to win both the Pacific Classic and Jockey Club Gold Cup, each valued at $1,000,000.

Borrego's final career race was the Breeders' Cup Classic, also held at Belmont that year, but he was unable to replicate his previous efforts as he ran 10th. Borrego was set to return to race as a five-year-old in 2006, but ankle surgery in March of that year pushed back his expected return date until late that summer. By April, Borrego had been officially retired from racing as he was not healing as quickly as expected.