Lock signed with the New York Yankees in 1958 but never appeared in an MLB game for the team. Instead, he was recalled from the Triple-A Richmond Virginians on July 11, 1962, and traded to Washington for veteran first baseman and pinch hitterDale Long. Lock played left field for Washington that season, but by early 1963 he became the Senators' regular center fielder, supplanting the colorful Jimmy Piersall, who was traded to the New York Mets.
His two most productive seasons were 1963 and 1964, when he hit 27 and 28 home runs and drove home 82 and 80 runs batted in respectively. Lock led American League center fielders in put-outs, assists and double plays turned in 1963, and all AL outfielders in assists the following year. As a batter, he finished second in the league in strikeouts in both 1963 and 1964.
