The second-place finisher, Andres Manuel Lopez Obrador, led a rally of thousands of protesters at the iconic Angel of Independence monument, where a banner referred to Pena Nieto: “Mexico hates you.”

Early in the day, bottle-throwing protesters tried to breach security barriers outside Congress before Pena Nieto’s arrival. Youths ripped down street-side payphones, tore up pavement and commandeered a garbage truck, ramming it against a tall steel security fence. Small fires burned from Molotov cocktails.

Police said seven protesters were injured in the morning. They denied reports that one man died from head injuries after a homemade bottle rocket struck him. No tally was offered for afternoon violence.

Inside the chamber, leftist lawmakers unfurled a huge black and white banner and held up giant placards decrying Pena Nieto’s inauguration. “Mexico in Mourning,” the banner said. “Teleprompter president, No Need to Assemble,” another said.

Despite the unruly scenes, the inauguration proceeded far more smoothly than in 2006, when months of street blockades and political turmoil followed a hotly contested presidential race that saw the National Action Party (PAN) and its then-leader Felipe Calderon barely edge out Lopez Obrador.

Signs of how Pena Nieto will govern became clearer on Friday when he named his Cabinet. Pena Nieto picked a mix of technocrats, former PRI governors and politicians linked to a former PRI president, Carlos Salinas de Gortari (1988-1994), who is at once reviled for corruption and admired by his countrymen.

He picked as the No. 2 man in the government a lawyer and longtime colleague, Miguel Angel Osorio Chong, who takes the Interior Secretariat portfolio. Osorio Chong, 48, is a former governor of Hidalgo state.

Pena Nieto put a Yale-trained economist, Jose Antonio Meade, in charge of the foreign secretariat, signaling that trade will become a focus of foreign affairs. And he tapped an enemy of the powerful teachers union leader, Elba Esther Gordillo, to head the education secretariat.

He pulled at least three people from outside the PRI into his Cabinet, including Meade, who held the finance portfolio under Calderon until Friday.

Yet to be seen is how far Pena Nieto may go in opening up the oil sector. Mexico, which is the world’s No. 4 oil producer, has seen production drop steadily in the last decade.

The state Petroleos Mexicanos, or Pemex, is the biggest contributor to Mexico’s federal budget. Pemex lacks both capital and know-how for intensive development of deepwater offshore reserves and reserves on land that require new technology for extraction.