Benedict waved to the crowd upon arrival as he stood in the back of a white popemobile, and they cheered and waved back. A crowd of 46,000 was expected, and the demand for tickets doubled the supply, organizers said.
The pope, wearing elaborate scarlet vestments, led the service from an altar erected in the center field of the recently inaugurated baseball stadium.
Barbara and Michael Loh of Williamsburg, Va., sat alone in the stands taking in the scene. They were among the first to arrive.
"I've been Catholic all my life and ... my dream has always been to see the pope," said Barbara Loh, tearing up.
At 5:45 a.m., more than four hours before the Mass, it was standing-room only on subways. Vendors hawked Vatican flags and souvenir buttons, but there were few takers as people hurried toward the stadium.
For others, there was nothing more important than getting in, and many people without tickets stood outside the subway station with signs pleading for extras.
Patty Trail, 54, pastoral associate at a church in Virginia Beach, Va., drove overnight to bring two priests to the Mass. She didn't have a ticket but said she was happy to at least be in the vicinity of the pope.
"Just to be out here, just to be in the presence," she said. "D.C. feels different."
Benedict spent the first full day of his U.S. journey Wednesday sharing a platform with President Bush and laying out his analysis of the American church to the nation's bishops.
Before Benedict's arrival, polls showed most Americans knew little or nothing about him. Those who have watched him so far have found a German-born pontiff who speaks excellent English, appears vigorous for his 81 years, mostly prefers script to spontaneity and displays a keen sense of the critical issues facing his 65 million-member American flock.
The pope's presence has deeply touched the devout. One young woman, awaiting his arrival at the basilica where he addressed the bishops, began weeping at first sight of the pope's motorcade, which was projected on a large screen. He was 10 minutes away.
Elsa Thompson of Washington, D.C., who as a basilica tour guide knows the stories behind nearly every mosaic and stained-glass window, said that when she looks at Benedict, she sees a moral authority and a clear voice in a confused world.
Yet she too wonders how the scholarly pontiff's message will translate Thursday in a baseball stadium, as Catholics from around the country are introduced to him in person.
"I watched him on TV at the White House, and I thought, 'How many people actually grasp what he's saying?' -- including me," Thompson said. "Yet at the same time, I felt challenged, because he is a teacher."
After his appearance at the stadium Thursday, Benedict will address Catholic educators and meet with leaders of other faiths.