Riley was promoted to his regional position in April last year when Ogilvy Group restructured OgilvyOne's regional management following the expansion of regional president of OgilvyOne Kent Wertime's role to include president of Ogilvy & Mather Japan.
The move further saw the promotion of president of OgilvyOne China and Ogilvy & Mather Group Shanghai, Chris Reitermann, to head up OgilvyOne in North Asia, managing the agency in China, Hong Kong, South Korea and Taiwan.
Mouritzen also assumed his post in April as part of the agency's wider plan to promote him to MD at the start of 2010. He replaced Anne Davis, who returned to Europe.
Mouritzen currently reports to Riley as well as group chairman of Ogilvy & Mather Singapore Stephen Mangham.
The news comes as OgilvyOne Hong Kong also reshuffled its management team, promoting business director Greg Carton to director of client service and group AD Sandy Ling to business director.