Rene Juarez Cisneros, president of the Institutional Revolutionary Party (PRI), addresses supporters at the party's headquarters in Mexico City, Mexico July 1, 2018. REUTERS/Ginnette Riquelme

MEXICO CITY (Reuters) - The head of Mexico’s ruling Institutional Revolutionary Party (PRI) stood down on Monday after the party’s record defeat in the July 1 presidential election, reducing the long-dominant force of Mexican politics to a fraction of its former strength.

Battered by corruption scandals, surging violence and poor economic growth, the centrist PRI was trounced by Andres Manuel Lopez Obrador, a veteran leftist and staunch critic of the establishment who has pledged a major shakeup of politics.

The PRI, which has ruled Mexico for 77 of the last 89 years, secured just 16.4 percent of the vote and saw its representation in Congress cut by about three-quarters.

Announcing his departure at a news conference, PRI leader Rene Juarez said the scale of the loss meant the party would have to take a hard look at itself.

“The future transformation of the PRI should be the size of the current defeat,” said Juarez, who only took over in May. By then, the polls showed the PRI was heading for a huge reverse.

Claudia Ruiz Massieu, the party’s secretary general, will take over the PRI leadership. A niece of former Mexican President Carlos Salinas de Gortari, Ruiz Massieu served as minister for tourism and later foreign minister under outgoing President Enrique Pena Nieto.