He was a member of the Boston side that won the inaugural 1903 World Series. Despite being a gifted defensive player, Ferris committed an error in the top of the first inning of the opening game of the series, fumbling a ball hit by Pittsburgh's Kitty Bransfield, and in doing so committed the first error in World Series history. He knocked in all of Boston's runs in the final game, which they won 3–0. Boston repeated as pennant winners in 1904, although no World Series was played that year. Ferris hit only .213 that season, and the team fell down the standings over the next years as its star players began to show their age. By 1906, Boston was in last place with a 49–105 record. Ferris was one of the team's few bright spots, playing excellent defense and ranking among American League leaders in extra base hits.