15-man Royal Rumble , earning a shot at the WWE Championship At No Way Out 2004 , Guerrero defeated the WWE Champion Brock Lesnar in the main event with help from Goldberg at WrestleMania XX he kept his title by beating Kurt Angle . At No Way Out , Guerrero defeated Lesnar in the main event to win the WWE Championship . His next feud was with Kurt Angle , whom he defeated at WrestleMania XX to retain his title in his first big defense .