He is currently one of the USTA's select "Master Professionals" and devotes most of his time coaching, participating and directing charity events and clinics and other tennis related projects.

In March 1964, Holmberg won the Altamira International Invitation in Caracas, Venezuela, respectively defeating Nikola Pilić, Rafael Osuna, Manuel Santana, and then Roy Emerson in the final.

The same month, he won the Southampton Invitation tournament on grass in Long Island, New York, defeating Jaime Fillol, Ray Moore, and Gene Scott.

He won numerous international doubles titles with many prominent players such as Barry MacKay (in Davis Cup), Pancho Gonzalez, John Newcombe, Tony Roche, Bob Mark and Arthur Ashe.

He was a member of Tennis Magazine's Instruction Advisory Board, which consisted of the top playing and teaching pros in the game for its duration of 19 years.