López led the Mexico City Reds to the 1974 Mexican League World Series, then made a brief MLB debut with the Kansas City Royals before returning to the Mexican League. López was named the 1977 Mexican League Most Valuable Player (MVP). He returned to the major leagues with the St. Louis Cardinals in 1978 and pitched for the Detroit Tigers between 1979 and 1985. López finished seventh in the Cy Young Award voting in 1979. He earned a 10–1 record and 14 saves for Detroit's 1984 World Series championship team.