Timlin made 76 appearances during the 2004 season; he had a 5–4 record, with one save and a 4.13 ERA. On September 3, he made his 800th major league appearance, becoming only the 29th pitcher in major league history to reach that mark. In the postseason he appeared in three games of the ALDS against the Anaheim Angels, five games of the ALCS against the Yankees, and three games of the World Series against the St. Louis Cardinals. In those 11 games, he pitched innings, facing 56 batters while striking out seven and giving up seven walks, 15 hits, and eight runs. With Boston's sweep of St. Louis in the World Series, Timlin earned the third championship of his career.