Hoerner was used exclusively in relief during his 14-year big league career. He appeared in 493 games, and during his first six full seasons (1966–1971) had one of the lowest combined ERAs among all major league relief pitchers (2.16).
Hoerner was drafted by the Cardinals from the Houston Astros in the 1965 rule V draft, and this led to him being part of two pennant-winning teams, including the 1967 World Series champions. In Game 3 of the 1968 World Series he became the first player in MLB history to get a hit in a World Series without having collected a hit in the regular season. In four seasons with St. Louis (1966–1969) Hoerner pitched in 206 games with a 19–10 record and 60 saves. He ranked in the National League top ten all four seasons for saves, and three times for games finished. On July 22, 1966 at Wrigley Field he hit his only major league home run, a three-run shot, against Hall of FamerFerguson Jenkins. During this time, he also tied a National League record for relievers with six consecutive strikeouts vs. the Mets on June 1, 1968.[3] He also appeared in five World Series games for the Cards, with a 0–1 record and one save.
Hoerner was traded to Philadelphia as part of the Curt Flood deal[4] on October 7, 1969. He made the National League All-Star team in 1970, and his .643 winning percentage ranked sixth in the league. During 1971 that year he gave up Willie Mays' major league-leading 22nd and last career extra-inning home run at Candlestick Park. In 1971, at age 34, he finished the year with a 1.97 ERA, and his effectiveness declined after that season. However, he later gave up Willie McCovey's N.L. record-breaking 17th grand slam in 1977 at Riverfront Stadium. His final major league appearance was on August 5, 1977. At the age of 40, he was the second-oldest player to appear in a National League game that season.
In 1985, Hoerner was acquitted of reckless and negligent operation of a motorboat, charges stemming from a collision on the Lake of the Ozarks that killed two 25-year-old boaters.[5]