Kammala jumla mai zuwa: Baltimore Colts ne suka zaɓa Nelson a zagaye na goma sha ɗaya na NFL Draft na 1957. Bayan ya buga duka kwata-kwata da kuma karewa a kwaleji, Colts sun sanya shi dan wasa mai karewa. Nelson ya fara wasanni 12 a kakar wasa ta farko, tare da hanawa 5 don yadudduka 29. A kakar wasa ta gaba, Nelson zai yi rikodin 8 da aka kama don 199 yadudduka da 1 touchdown. Colts za su ci gaba da lashe gasar zakarun na NFL a cikin abin da ya kasance wasan farko na NFL da aka yi a cikin lokaci mai tsawo kuma tun daga lokacin ya zama sananne a matsayin "The Greatest Game Ever Played". Colts za su maimaita a
1959 kuma a cikin shekaru bakwai na aikinsa tare da Colts, Nelson zai tara jimillar 33 da aka kama don 378 yadudduka da kuma 3 touchdowns. Colts sun yi musayar Nelson zuwa New York Giants don kakar 1964, ta ƙarshe a cikin NFL.