About 100 parishioners filled Santa Maria della Vittoria, the church designated by the Vatican for O'Malley to preach in when in Rome, to see the candidate for pope, who was introduced by the Rev. Rocco Visca.
"May this be your last visit here as cardinal, and may we be the first church you visit as the next pope," Visca said.
O'Malley is just one of 115 contenders, USA Today said.
The newspaper said O'Malley seemed to shrug off the papal references and didn't mention the conclave except to imply that he'd be going back to Boston after it concludes.
Deacon Tim MacDonald of Boston, who is studying in Rome, said he is excited about O'Malley's chances.
"The people of Boston have a great admiration for him, and just having any American would be amazing," he said. "But the conclave is always a mystery."