Joseph Diaz has had a total of four losses in his professional boxing career so far — two of them in title bouts and two in non-title bouts. He suffered his first loss against Gary Russell Jr. via 12 round unanimous decision on May 19, 2018, which ended his 26-fight win streak. He has never been stopped, all his losses came via decision.
Mercito Gesta, William Zepeda, Devin Haney, and Gary Russell Jr. are the four boxers who have beaten Diaz.
This is the first loss in Joseph Diaz' career. Diaz lost to Gary Russell Jr. via 12 round unanimous decision on . He was fighting for Russell Jr.'s featherweight WBC title, he was 25 years old with a record of 26-0. Russell Jr. was 29 years old with a record of 28-1.
On Diaz lost to Devin Haney via 12 round unanimous decision. He was fighting for Haney's lightweight WBC title, he was 29 years old with a record of 32-1-1. Haney was 23 years old with a record of 26-0.
On Diaz lost to Mexican boxer William Zepeda via 12 round unanimous decision in a non-title bout. He was 29 years old with a record of 32-2-1. Zepeda was 26 years old with a record of 26-0.
On Diaz lost to Filipino boxer Mercito Gesta via 10 round split-decision in a non-title bout. He was 30 years old with a record of 32-3-1. Gesta was 35 years old with a record of 33-3-3.