In 1984, Martínez batted .303 with 15 home runs and 84 walks for the Wausau Timbers of the Class A Midwest League. Martínez played for the Chattanooga Lookouts of the Class AA Southern League and Calgary Cannons of the Class AAA Pacific Coast League (PCL) in 1985, batting .258 in 111 games for Chattanooga and .353 in 20 games for Calgary. He returned to Chattanooga in 1986 and had a .960 fielding percentage, which led all third basemen. Playing for Calgary in 1987, Martínez had a .327 batting average, 10 home runs, and 31 doubles in 129 games. He led Calgary in batting average, as well as hits, doubles, batting average, on base percentage, games played, and walks.