In 1979–80, Crombeen spent the entire season with the Blues, getting 22 points (10G-12A) in 71 games, and appeared in his first NHL playoffs, going pointless in 2 games. Crombeen then registered 23 points (9G-14A) in 69 games in 1980–81, and chipped in with 3 goals in 11 playoff games, including a goal in double overtime that clinched the Blues' first-round series against the Pittsburgh Penguins.
In 1979–80, Crombeen played the entire season with the Blues, scoring 22 points (10 goals-12 assists) in 71 games and participated in his first NHL postseason, going scoreless in 2 games. Crombeen then recorded 23 points (9 goals-14 assists) in 69 games in 1980–81, and contributed 3 goals in 11 playoff games, including a goal in double overtime that sealed the Blues' first-round series against the Pittsburgh Penguins.