Having defeated Jesus Poll by a decision in twelve rounds and Troy Dorsey by a knockout in six, he was matched, on March 23, 1993, with Louie Espinoza, a former two-time world featherweight champion.

On September 10, 1993, Leija participated at one of the Alamodome's first ever events, when he challenged Azumah Nelson for the WBC super featherweight title.

After twelve rounds, Nelson had been announced as the winner by a split decision, only to find out twenty minutes later that a judge had miscalculated his scoring card, and the fight was really a draw.

Leija became the WBC super featherweight champion when he defeated Nelson by a twelve-round unanimous decision in Las Vegas.

After a string of wins against relatively insignificant competition, Leija won the NABF lightweight title, defeating Joel Perez by a decision in twelve rounds on January 20, 1998.

Leija was dropped in rounds six, eight and nine before the fight was stopped, with Mosley retaining the world title by a ninth-round knockout win.

Next followed another HBO televised fight, when Leija fought Ivan Robinson, who had twice beaten Arturo Gatti, on November 11 at Las Vegas.

Camacho Jr. was initially announced as the winner by a technical decision, but the Leija team formally protested the result with the New York State Athletic Commission.

Micky Ward was being considered for a fight with WBC, WBA and IBF world light welterweight champion Kostya Tszyu.

Leija then proceeded to move to Australia for six months, to get acquainted with the country and its climate before his challenge of Tszyu, scheduled for January 19, 2003.

Leija produced what some viewed as a minor upset by beating his much younger rival by a ten-round split decision.