Keys was introduced by Valerie Jarrett, a senior adviser to the president, who warned that Republican nominee Mitt Romney would push for "trickle-down" economic policies that she said have failed the country.
"To be very blunt, Mr. Romney is not looking out for you," Jarrett said.
U.S. Rep. Debbie Wasserman Schultz, chairwoman of the Democratic National Committee, egged on the Convention Center crowd when it booed Romney.
"I can completely understand that sentiment," she said.
Outside, about a dozen tea party activists had their own boos for her, continuing to criticize comments she made in January when she called for a more civil national debate about a year after the shooting of U.S. Rep. Gabby Giffords, an Arizona Democrat.
The tea party is demanding an apology because Wasserman Schultz cited that movement as an example of uncivil debate.
The Romney campaign, anticipating the visit by Keys, Jarrett and Schultz, organized a LOVE Park rally earlier in the day to change the conversation.
Chester County Sheriff Carolyn "Bunny" Welsh and Renee Amoore, deputy chairwoman of the state Republican Party, accused Obama of using federal stimulus funds and funding for green energy projects to reward his political "cronies."
Welsh noted that the unemployment rate for women in Pennsylvania increased from 7 percent to 8 percent during his time in the White House.
"Barack Obama was trained in Chicago politics," Welsh said. "What is that? Pay-to-play and support your friends."
Both women called unequal pay for women a problem but were not bothered that Romney has declined to take a position on the Lily Ledbetter Fair Pay Act.
"He will take a position, sooner rather than later," Amoore said. "There is a long time before November. And he has plenty of time to give his position."
Romney spokeswoman Kate Meriwether later claimed women "suffered disproportionately" in Obama's handling of the national economy.
"Of course Mitt Romney supports pay equity for women and is not looking to change current law," Meriwether said. "The real question is whether President Obama supports jobs for women."
Contact Chris Brennan at 215-854-5973 or email him at firstname.lastname@example.org. Follow him on Twitter @ChrisBrennanDN and read his blog, PhillyClout.com.