Prior to the 1952 season, López was acquired by the
Philadelphia Athletics from the
Drummondville Cubs of the Provincial League for $1,500 ($ today). Throughout his professional career, he played in the Panama winter league where he won three batting titles and regularly led the league in home runs. López developed in the A's farm system, and when the team relocated to Kansas City in 1955 he was called up to the major league club. López made his major league debut in 1955. López was the team's regular third baseman, and was the youngest regular starter on the team. In 1956, the team finished with a 52–102 record, but López had a career-high 153 hits. In his early years, black and white players did not room together on the road, so he roomed with
Vic Power even though Power's closest friend on the team was
Clete Boyer. In 1957, he had a 22-game
hitting streak, which is the all-time Kansas City Athletics team record for the thirteen seasons the franchise played there. López finished in the top-10 in the
American League in both games played and at bats in the 1956 and 1958 seasons, and led the league in
sacrifice flies and times
grounded into double plays in 1958. López also was in the top 10 in doubles and runs scored in 1958 and in sacrifice hits in 1956. During his career with the Athletics, he hit .278 with 67 home runs and 269 RBIs, and scored 298 runs. However, his talents were wasted on a team that never finished above sixth place. On May 26, 1959, he was traded with
Ralph Terry to the
New York Yankees for
Johnny Kucks,
Tom Sturdivant, and
Jerry Lumpe. Baseball writer and Kansas City Athletics fan
Bill James wrote that López was as bad a defensive player as you would ever want to see. The authors of
The Great American Baseball Card Flipping, Trading and Bubble Gum Book declared López "the all-time worst fielding major league ballplayer". ==New York Yankees (1959–1966)==