He played for them until 1968, before joining the Pittsburgh Pirates (1969–70), St. Louis Cardinals (1970), Boston Red Sox (1970) and Toronto Blue Jays (1977).

On June 17, 1965, Hartenstein performed one of the most impressive pitching feats in Texas League history, in a game against the Austin Braves as the starter, the Spurs had a 1–0 lead going into the ninth inning when he gave up a tying run.

Hartenstein was traded, along with Glenn Redmon, from the Chicago White Sox to the San Francisco Giants for Skip Pitlock on February 8, 1973.

[2] In a six-season career, Hartenstein posted a 17–19 record with a 3.63 ERA and 23 saves in 187 relief appearances, including 88 games finished, a 1.52 strikeout-to-walk ratio (135-to-89), and 297 innings of work.

After six years pitching in the minors, Hartenstein appeared in his last major league season with the expansion Toronto Blue Jays in 1977.