He was selected as the Yankees Minor League player of the Year in 2000 when he was a combined 14–5 with a 2.85 ERA in 28 starts for Double-A Norwich and AAA Columbus.

He signed as a free agent with the Texas Rangers on June 16, 2003, and appeared in 5 games (2 starts) for the AAA Oklahoma RedHawks before he was released on July 14.

Keisler signed as a free agent with the New York Mets on February 17, 2004, and played the 2004 season with the AAA Norfolk Tides.

He signed with the Cincinnati Reds as a free agent on November 12, 2004, and began the season with the AAA Louisville Bats where he was 5–2 in 12 appearances (7 starts) for a 2.88 ERA.

The Oakland Athletics signed him as a free agent on January 5, 2006, and he made 11 appearances (all out of the bullpen for the A's in 2006, with a 4.50 era and no record.

On March 3, 2011, he attended an open tryout, sponsored by the Los Angeles Dodgers and was signed to a Minor League contract [1] He was assigned to the AAA Albuquerque Isotopes, where he appeared in 23 games (19 starts) and was 7–7 with a 4.67 ERA.