Born in the Esbjerg suburb of Guldager, Bertelsen started playing football with small-time club Sædding-Guldager.
He was a hard-working defensive midfielder, and helped the team win promotion to the top-flight Danish 1st Division.
[2] In the 1st Division, Bertelsen helped Esbjerg finish third in 1977, second in 1978, and finally win the 1979 Danish football championship.
Bertelsen made his international debut with the Denmark national under-21 football team in May 1975, and played five under-21 games until October 1975.
Bertelsen had a somewhat anonymous role in the defensive midfield,[1] though his work rate made him an integral part of the team.