GUATEMALA CITY — Sergio Bacini is a music producer, a tattoo artist and a D.J. When the five-month protest movement that swept out Guatemala’s president last week seemed to flag during the summer, he knew how to revive it: He organized a rock concert.

A popular local band, Alux Nahual, headlined the daylong festival, playing to crowds massed in the central plaza where Guatemalans had been demonstrating since April against their government’s corruption and dysfunction.

The protesters have won the first round by ousting the president. But protest movements often fizzle after the euphoria of early victory, and Guatemala’s will likely need more than rock concerts to keep it going. “Now more than ever, we have to continue applying pressure, and the activists have to keep agitating so that this movement holds on and doesn’t fall away,” said Mr. Bacini, 25.

Otto Pérez Molina, the retired general who resigned as president, will return to a courtroom on Tuesday, when a judge will decide whether he must stand trial on charges that he ran a vast customs fraud ring. A suddenly diminished figure, he was already old news, though, as people headed to the polls on Sunday for presidential and congressional elections.