In September 2003, Devlin turned down an initial loan move to West Ham United in favour of a three-year contract with First Division Watford, managed by Ray Lewington, who were in need of a winger after the death of Jimmy Davis. Devlin's wages and the £150,000 fee were funded on behalf of the financially struggling club by a "mystery benefactor", who was later confirmed to be former chairman Sir Elton John. He was sent off before half-time for two mistimed tackles in his second match, which Watford lost to a late Derby County goal, but by the end of the campaign, in which the team finished 16th, no outfield player had made more appearances. Writing on Watford fansite "Blind Stupid and Desperate", Matt Rowson highlighted how Devlin's "experience, aggression, and tricksiness was employed to the irritation of opponents who regularly paid the compliment of double-marking him", but also thought him "Not the player to misplace or mistime a pass to, one suspects, nor a player that many referees look forward to officiating."