Emanuelson is a product of Ajax's youth system, joining them from Voorland SC. Having progressed through the club's youth system, he signed his first professional contract, keeping him until 2006. Having been called up to the first team on two occasions, on 24 February 2005 Emanuelson made his Ajax debut, coming on as a 79th minute substitute, in a 3–1 loss against Auxerre in the second leg of the UEFA Cup Round of 32. He made his debut during the 2004–05 season on 10 April 2005, coming on as a 78th minute substitute, in a 4–2 home win over AZ Alkmaar. Emanuelson later made three more appearances, adding up his tally to five at the end of the 2004–05 season.