Johnson joined the Kansas City Wizards in the 2006 season and scored on his debut.
He received his first cap and scored his first goal for the senior US national team against El Salvador on 9 October 2004, becoming one of an elite group of American players to get his first international goal in a World Cup Qualifier. He then scored a hat-trick in his second appearance, all in a 17-minute span against Panama, just four days later. Johnson scored a total of seven goals in his first six World Cup Qualifiers and has been the source of much speculation linking him with a move to the Premier League.