O’Brien appeared in seven games for the Cardinals during the 1978 season, going 0-2 with an earned run average of 4.50 over 18 innings, with two of those games as a starter.
In 1979 he’d be back on a Major league mound, albeit for only six appearances, going 1-1 with a bloated 8.18 ERA over eleven innings, all out of the bullpen.
He’d go on to play two more seasons in the Minor Leagues for both the Atlanta Braves and Houston Astros organizations, but never get back to the Big Leagues, retiring as a player after the 1981 campaign.
All told, he’d finish his career with a career 1-3 record, with a 5.90 ERA over 13 appearances and 29 innings of work under the Major League sun.