The lefthander from California was acquired from the Braves after the 1967 season along with Denis Menke for infielders Chuck Harrison and Sonny Jackson in one of the better trades by the Astros during that era. In four seasons with Houston, Lemaster compiled a 30-46 record with a 3.40 ERA and six saves while pitching both as a starter and reliever.

Lemaster was sold to the Expos in 1972 and pitched one season there. Overall in eleven seasons, he posted a 90-105 mark, including 66 complete games, 14 shutouts and a 3.58 ERA.