For the next two years, Cronin remained solely in goal, starting 27 matches and being named first-team All-West Coast Conference as a junior.

Cronin joined Major League Soccer side D.C. United on 9 October 2009 on loan from Portland until the end of the 2009 MLS season.

Cronin enjoyed a strong season with Portland in 2010 appearing in 28 league matches, in which he posted a .79 goals against average which included 12 shutouts.

On October 19, 2010, Cronin was named as one of the first four players to be signed by the Portland Timbers ahead of their expansion into Major League Soccer in 2011, along with Bright Dike, Ryan Pore and Eddie Johnson.

As a teenager, Cronin trained with the Under-17 United States national team at the USSF's Bradenton Academy, alongside players like Landon Donovan, DaMarcus Beasley, and Bobby Convey.