The deal also gives Dentsu access to companies working with the Asian Basketball Confederation and the Asian PGA Golf Tour. Presently, soccer accounts for about two-thirds of WSG revenues.
Dentsu was unable to comment on the move when Media went to press.
In a statement, the Japanese agency said the tie-up would enable it to promote and develop sports business in the Asia region together with WSG.
World Sports Group Holdings is headquartered in Singapore, with a regional office in Hong Kong. Its Japanese operations will now be run by Dentsu.
WSG founders Seamus O'Brien and Tony Morgan retain a majority share in the group.
O'Brien, WSG president, said Asian audiences were flocking to local sports, and expected sponsorship money to follow. "If you add up figures for the Premier League it doesn't get close to Asian fans watching Asian sports," he said.
WSG employs around 100 people.
Dentsu grows stake in sport specialist World Sport Group
Dentsu has extended its sports marketing capability by taking a 30 per cent stake in World Sport Group Holdings, which owns the main marketing rights for the Asian Football Confederation, organisers of this month's Asian Cup in China, through its World Sports Group (WSG) subsidiary.