They were there to try to persuade Francis to come to Philadelphia next year for the eighth World Meeting of Families: an international, Vatican-sponsored, five-day event expected to draw hundreds of thousands of visitors to the city.
The archdiocese learned two years ago it had been chosen to host the meeting in September 2015.
After circling the square for 20 minutes, Francis settled into a plain, upholstered chair under a metal canopy on the basilica front steps.
He greeted a family with a seriously ill young daughter, and visiting clergy, then Corbett led the Pennsylvania delegation - some with trembling legs, they later acknowledged - as they filed forward to offer Francis their personal invitations.
"We had a private audience in front of 100,000 people," Corbett joked afterward.
Said his wife, Susan: "We came as joyful pilgrims and left ecstatic pilgrims." The Corbetts presented Francis with handmade Mercer tiles from Bucks County bearing the names of the four evangelists, along with a book about Philadelphia's celebrated outdoor murals and other mementos of the commonwealth.
"He's a very joyful man," said Nutter, who presented the pope with the jerseys of his high school alma mater, St. Joseph's Prep, and those of the city's five major-league sports teams. (Francis did not try one on.)
No audience lasted longer than a minute. The others in the delegation bowed or shook hands briefly with the pontiff, told him of their admiration, and invited him to Philadelphia. Some also presented him with small gifts.
"I didn't expect to be so overwhelmed by the power of his personality and the power of his office," said Dan Hilferty, president and CEO of Blue Cross-Blue Shield of Pennsylvania, who was joined by his wife, Joan.
They found themselves welling up as they approached, he said, but found Francis humble and authentic.
Hilferty, cochair of the archdiocesan executive leadership group seeking to raise at least $15 million for the event, said as he watched Francis circling the square thronged by thousands of cheering pilgrims, "I couldn't help thinking of the possibilities for Philadelphia."
Robert J. Ciaruffoli, president of the eighth World Meeting of Families, described his brief encounter as powerful.
"My legs started shaking as I approached," Ciaruffoli, CEO of the Philadelphia accounting firm Parente-Beard, said. "As I got closer, I saw he was grinning ear to ear." Ciaruffoli, too, said he urged Francis to visit Philadelphia for the World Meeting.
More than 18 months in the planning, Wednesday's meetings were not the extended private sessions at Francis' residence the delegates had envisioned Sunday night as they boarded the plane for Rome.
Late Tuesday, the Vatican sent word the delegates would meet Francis instead at the public audience. Although Chaput had cautioned Monday the pope might be too busy for private time, the official explanation Wednesday was that the Vatican wanted the Philadelphia news media to witness and report on the visit.
"We were not at all disappointed," a broadly grinning Corbett said at a news conference after the public audience. "I think he was excited to see this delegation."
Nutter, who presented the pope with an invitation signed by the Prep's entire junior class, said afterward, "I'm ecstatic."
Both men said they got little more than noncommittal smiles and nods from Francis when they implored him to visit Philadelphia. But each said several times he was optimistic the pontiff would honor tradition by saying Mass at the conclusion of the World Meeting.
Said Nutter, "It couldn't have gone better."
Among the items presented to Pope Francis:
A replica Liberty Bell with his name on it.
Personalized sports jerseys.
Jersey and hat from St. Joseph's Prep, Mayor Nutter's alma mater.
Four ceramic tiles representing the four gospels, made by Moravian Pottery & Tile Works in Doylestown.
A first-edition copy of Philadelphia artist Jerry Pinkney's children's book Noah's Ark.
Philadelphia Murals and the Stories They Tell, inscribed by Jane Golden.
Letters from students of Good Shepherd Elementary School in Camp Hill, Pa.
Find more coverage of the Philadelphia delegation's visit, including more photographs by David Maialetti at www.inquirer.com/rome