Lastra won the first twelve fights of his career, including six first round knockouts, before losing for the first time, in September 1976, against Carlos Hernandez.

Following this defeat, Lastra won eight successive fights in Santander, before beating Isidoro Cabeza for the Spanish featherweight title.

In December 1977 Lastra challenged Rafael Ortega for the WBA featherweight title in front of an estimated crowd of 6,300 in Santander.

Ortega, a Panamanian who had won the title earlier in the year, was knocked down in the second round after a left jab to the nose.

After four losses in a row, including two Spanish title fights, Lastra fought for a final time in July 1982, losing in the fifth round against Amalio Galan.