Cronin started 28 matches for Portland in the USSF Division-2 Pro League in 2010, anchoring a backline that ranked second in the league in goals allowed. The California native ranked among the league leaders in shutouts (12), minutes played (2,509), and third in goals against average (0.79). In 2009 Cronin was named USL First Division Goalkeeper of the Year with the Timbers, leading the club to a record 24-match unbeaten streak during the regular season.
During his time in Portland, Cronin was loaned to D.C. United at the end of the 2009 campaign, making his first appearance on October 17 in a shutout victory over Columbus. Cronin started two regular season matches for United, posting a 1-0-1 record, while appearing in a CONCACAF Champions League match against Mexican side Toluca on October 20. Prior to 2009, Cronin spent four seasons with the Los Angeles Galaxy, earning his first career victory on April 29, 2006 in a 3-2 win over Real Salt Lake. His best year in Los Angeles came in 2008, when Cronin started 22 matches before injuring his hand on August 30 against New England.
Cronin was selected tenth overall by San Jose in the 2004 MLS SuperDraft after a three-season college career with Santa Clara University. After leading the Broncos to West Coast Conference titles in 2001 and 2003, Cronin did not see any first team action in his first and only MLS season with the Earthquakes.