In 2003, Payton enjoyed his most productive season with career highs in home runs (28), RBI (89), runs (93), hits (181), doubles (32), on-base percentage (.354), slugging average (.512), at bats (600) and games played (157), and added a respectable .302 batting average. He was signed by San Diego as a free agent at the end of the season. But Payton had a subpar 2004 season batting .260 with eight homers and 55 RBI in 143 games. In December, he was sent to Boston for Dave Roberts and took over Roberts' role as the team's fourth outfielder.