The special election was held after former Gov. Naoki Inose resigned in December amid scandal one year into his term, the newspaper reported.
Masuzoe, 65, defeated former Prime Minister Morihiro Hosokawa, former president of the Japan Federation of Bar Associations Kenji Utsunomiya, and former Chief of Staff of the Air Self-Defense Force Toshio Tamogami.
Masuzoe ran on a campaign focusing on social welfare and implementing measures to accommodate for the falling birthrate and rapidly aging population. He also pledged to make the 2020 Olympics in Tokyo the "best in history."