Under legendary coach Danny Litwhiler, he was a second-team All Big Ten Baseball Team selection in 1982 and received the Steve Garvey Sportsmanship Award.

After going 12–8 with a 2.36 earned run average with the Fort Lauderdale Yankees in 1983, Birtsas' 1984 season was delayed by a leg injury in spring training.

After the season, he was packaged with Jay Howell, Stan Javier, José Rijo and Eric Plunk in a trade to Oakland for Rickey Henderson.

With the A's already losing 10–0 to the Boston Red Sox, Birtsas made his major league debut on May 3, and pitched the final two innings without allowing any more runs while striking out three.

He allowed five earned runs on two hits (including a grand slam by Brian Downing) and three walks in just one inning in his first appearance of the season.

After splitting the 1987 season between Tacoma and double A Huntsville, Birtsas was again packaged with José Rijo, this time to the Cincinnati Reds for Dave Parker.

With his record standing at 1–3 with a 4.50 ERA, he was optioned back to triple A at the end of August,[9] but an injury to Rijo helped keep him in the majors through the rest of the season.

[14] The relief corp of the Reds earned the nickname "The Nasty Boys" along the way, and lived up to this reputation by leading the National League with 46 saves, and compiling 385 strikeouts.

With no major league teams bidding on his services, Birtsas signed with the Tokyo Yakult Swallows of Nippon Professional Baseball for the 1991 season.