Officials at Sunday's race, stunned to see an Argentine surge past Kenyan leader and title holder Julius Karinga, ordered Mastromarino to leave the race around the 37km mark.
"They thought I was an intruder. 'Get out of the race, get out. Don't stay there, this is a race'," Mastromarino told ESPN the officials had shouted at him.
They soon realised their mistake and Mastromarino, who had narrowly missed qualifying for the 2012 Olympics in London, went on to win in two hours, 15 minutes and 28 seconds with two Chileans completing the podium.
The previous Argentine winner was Oscar Cortinez in 2004.
Lucy Karimi maintained the Kenyan winning tradition with her third successive victory in the women's event.
Newcastle United soccer player Jonas Gutierrez took part to help highlight cancer research. The former Argentina winger is fighting testicular cancer.
(Writing by Rex Gowar; editing by Martyn Herman)
