He played for the Double-A Tulsa Drillers in 2010, pitching to a 8–5 record and a 4.01 ERA with 135 strikeouts in 161.2 innings of work.
[7] In 2012, Riordan split the season with Tulsa and Colorado Springs, pitching to a cumulative 4.37 ERA with 66 strikeouts in 94.2 innings of work.
[8] Riordan once again split time with the Double-A Tulsa Drillers and the Triple-A Colorado Springs Sky Sox in 2013.
On January 10, 2014, Riordan agreed to a one-year, $300,000 contract with the LG Twins of the Korea Baseball Organization.
He made 17 starts in 18 appearances for the Bluefish, pitching to a 3.62 ERA with five victories and 82 strikeouts in 112.0 innings before his contract was purchased by the Lamigo Monkeys of the Chinese Professional Baseball League.
On April 4, 2017, Riordan signed with the Bridgeport Bluefish of the Atlantic League of Professional Baseball.
On February 5, 2018, Riordan signed with the Somerset Patriots of the Atlantic League of Professional Baseball after his rights were acquired in the Bridgeport Bluefish dispersal draft.
On May 2, 2020, Riordan announced his retirement as an active player and that he'd accepted a role as a minor league coach in the Toronto Blue Jays organization.