Enrique Pena Nieto has taken the oath of office as Mexico's new president vowing to restore peace and security and take on the vested interests that have hindered economic prosperity.
As several hundred protesters threw fire bombs at police and smashed plate glass windows, Mr Pena Nieto marked the return of the Institutional Revolutionary Party, or PRI, with a 13-point plan heavy on old-party populist handouts but with reforms designed to boost the economy and modernise the education and justice systems.
"Mexico has not achieved the advances that the population demands or deserves," Mr Pena Nieto said in an inaugural speech unusual for its heavy emphasis on policy.
"It's time for us together to break the myths and paradigms and all else that has limited our development."
Inaugural events were marred all day by protesters opposed to the return of the PRI after a 12-year hiatus.
Inside and outside the congressional chambers where he took the oath of office, his opponents called his inauguration an "imposition" of a party that ruled for 71 years using a mix of handouts, graft and rigged elections.
At least 76 people were treated for injuries, including 29 who were taken to hospital, as the result of clashes between protesters and tear-gas firing police, the Red Cross said. City officials said 103 people were detained, including 11 minors.
Vandals smashed windows of stores, banks and a hotel and made bonfires of furniture dragged into the streets.
One bank office where all the windows were broken had the words Welcome Pena painted across the facade in green.
Mr Pena Nieto countered with a speech full of specifics, from creating an integrated crime prevention programme to ending the patronage and buying of teacher positions that rule the public education system.