In 1966, Stanley made the big league roster and began the season as the team's starting center fielder. In mid-May, he broke a bone in his left little finger when he fell at his home after washing his car. He returned to the lineup in mid-June and appeared in a total of 92 games, 82 in center field. He ended up leading the team with a .289 batting average and finished the season with a perfect 1.000 fielding percentage in 174 chances in center field. Stanley credited his improved batting in 1966 to acting manager Frank Skaff giving him more playing time in the second half of the season and boosting his confidence.