Guevara played on the 2001 St. Mary's team which won the 2001 NCAA Division II College World Series.

[citation needed] Guevara was selected by the Cincinnati Reds in the seventh round (201st overall) of the 2003 Major League Baseball Draft.

[citation needed] After signing with the Reds, Guevara began his career with the Billings Mustangs of the rookie league.

[citation needed] On December 6, 2007, Guevara was selected by the Florida Marlins in the Rule 5 draft and traded to the San Diego Padres the same day.

In five rehab appearances with the Triple-A Portland Beavers, Guevara pitched six scoreless innings, allowing two hits and striking out five.