The ruling conservative party has for the first time selected a female candidate to stand in the country's presidential election.
Josefina Vazquez Mota, 51, a former Education Minister, beat Ernesto Cordero, the preferred choice of President Felipe Calderon, in the National Action Party's primary election on Sunday.
She defeated Mr Cordero, the former Finance Minister, by almost 20 per cent but still faces an uphill battle in the 1 July election. Opinion polls put her well behind the front-runner, Enrique Pena Nieto, of the socialist Institutional Revolutionary Party, which has ruled Mexico for more than 70 years.
Ms Vazquez Mota's victory over Mr Cordero is an upset for party bosses who often have the final say in choosing candidates, and gives her a shot at becoming the first female president of Mexcio.