In 2015 he defeated champion California Chrome in the San Antonio Stakes and then won the Santa Anita Handicap, before being sidelined for the rest season with a hip injury.

[5] Shared Belief made his racecourse debut in a maiden race over six furlongs on the synthetic Tapeta Footings track at Golden Gate Fields on October 19.

[7] Over the same course on December 14, Shared Belief was moved up to Grade I class for the CashCall Futurity over a mile and a sixteenth and started favorite against eleven opponents.

Nakatani placed the gelding just behind the leaders before taking the lead in the straight and accelerating clear in the closing stages to win by five and three quarter lengths.

[8] In January 2014, Shared Belief was named Champion Two-Year-Old Male Horse at the Eclipse Awards, beating Breeders' Cup Juvenile winner New Year's Day by 115 votes to 99.

On August 24, Shared Belief contested the $1,000,000 TVG Pacific Classic Stakes at Del Mar Racetrack against older horses, going a mile and a quarter for the first time and attempting to emulate his sire Candy Ride, who won the race in 2003.

The gelding raced in midfield before moving up on the outside, taking the lead a furlong and a half out and drawing away to win by almost three lengths from the British challenger Toast of New York.

Shared Belief appeared to hamper the runner-up when hanging in towards the rail at the top of the stretch, but after a stewards' inquiry the result was allowed to stand.

"[12] In his narrowest victory to date, Shared Belief took on older horses and won the September 27 Awesome Again Stakes by a neck over Kaleem Shah's Fed Biz, trained by Bob Baffert.

Shared Belief was forced wide for nearly the entire race, notably by a second Baffert entry, the longshot Sky Kingdom, a riding tactic viewed negatively as "gamesmanship" in post-race press analysis.

"[16] On his final appearance of the year, Shared Belief was brought back in distance for the Grade I Malibu Stakes over seven furlongs at Santa Anita on December 26.

Carrying top weight of 123 pounds, he started the 1/2 favorite and won by a neck from Conquest Two Step after taking the lead inside the final furlong.

[18] Shared Belief began his third season in the San Antonio Stakes over nine furlongs at Santa Anita on February 7, which featured a much-anticipated clash with California Chrome.

In the straight, Shared Belief moved up to join California Chrome, took the advantage a furlong out, and drew away in the final strides to win by a length and a half.

[23] The horse was flown back to the west coast and as of 22 April 2015[update] was to be shipped to the Pegasus Training Center in Renton, Washington for 45 to 60 days of rehabilitation.