Montreal lost the draft rights to Patterson on a legal technicality: they sent him a contract offer that was not printed on official team letterhead, and he signed with the Arizona Diamondbacks for $6.075 million.

Patterson was traded back to the Expos prior to the 2004 season in exchange for Randy Choate, a left-handed relief pitcher.

Always filled with immense potential – he featured a fastball in the mid-90s (miles per hour) along with a big curveball and a sharp slider – Patterson started to realize it while pitching for Montreal in 2004, when he had a 3.57 ERA in April.

Patterson had a breakout season in 2005, posting a 9–7 record for Washington while setting career bests in ERA (3.13), innings pitched (198.3), and strikeouts (185) in 31 starts.

[2] Early in 2006, Patterson suffered an injury to his right forearm which had to be surgically repaired on July 20, and he did not return for the 2006 campaign.