Far more than in earlier GOP debates this summer, the candidates mixed it up in their first faceoff since Perry entered the race and almost instantly overtook Romney as front-runner in opinion polls. Those two - as well as other contenders on stage - sniped at one another, contradicted allegations and interrupted media questioners to demand opportunities to take each other on.
"Michael Dukakis created jobs three times faster than you did, Mitt," Perry jabbed in the debate's opening moments, referring to one of Romney's Democratic predecessors as governor of Massachusetts.
"As a matter of fact, George Bush and his predecessors created jobs at a faster rate than you did," Romney shot back at Perry, the 10-year incumbent Texas governor.
The debate was the first of three in as many weeks, at a time when the economy is struggling, unemployment is seemingly stuck at 9.1 percent and Obama's popularity is sinking in the polls - all events that could make the GOP nomination worth more than it appeared only a few months ago.
Perry and Romney stood next to each other on the debate stage at the Ronald Reagan Presidential Library, a setting that invoked the memory of the conservative Republican who swept to two terms as president. And for much of the evening, the two men were at the center of the action, largely reducing their rivals to the roles of spectators looking for a way into the action.
Former Utah Gov. Jon Huntsman sided with Perry when he turned to Romney and said, "47th just isn't going to cut it, my friend," a reference to the rank Massachusetts had among the 50 states in creating jobs during Romney's term.
But he also sought to rebut Perry's claim to be chief executive of the country's top job-producing state.
"I hate to rain on the parade of the great Lone Star State governor, but as governor of Utah, we were the No. 1 job creator during my years in service," Huntsman said.
Businessman Herman Cain, Minnesota Rep. Michele Bachmann, Texas Rep. Ron Paul, former House Speaker Newt Gingrich and former Sen. Rick Santorum of Pennsylvania shared the stage for the debate hosted by MSNBC and Politico.
Not surprisingly, the GOP contenders had little good to say about Obama, either his record on creating jobs or the health care law they have vowed to repeal if they win the White House. Perry was an exception, volunteering his praise for the presidential order that resulted in the death of Osama bin Laden in a U.S. military raid in Pakistan. He also said he was happy the U.S. prison at Guantanamo has been kept open.
On another foreign policy issue, Bachmann criticized Obama's decision to join an international military campaign in Libya.
Bachman also said she would provide the "strong, bold leader in the presidency who will lead" the effort to repeal the health care law passed at Obama's behest. "None of us should ever think that the repeal bill will just come to our desk," she said in a pledge that drew applause from the audience.
Gingrich resisted an effort to draw him into conflict with other Republicans on stage. "I'm frankly not interested in your efforts to get Republicans fighting each other," he said, sparking an even louder round of applause. He said all Republicans should "defeat efforts by the news media" to spark an internal struggle when the real objective is to defeat Obama in 2012.
But moments later, Cain said that after trying to defeat Democratic efforts to create national health care, "I'm running against Romneycare," the legislation that passed requiring residents of Massachusetts to purchase coverage.
Social Security produced more sparks, when Perry said the program was a "Ponzi scheme" and added it was a lie to tell young workers they will ever receive the benefits they have been promised.
Romney quickly referred to Perry's book, "Fed Up," in which the Texas governor said that by any measure the program was a failure. Perry also said states should be able to opt out of the program,' Romney added.
Perry was unrepentant - "You cannot keep the status quo in place and call it anything other than a Ponzi scheme," he said.
The Texas governor also made it clear he doesn't intend to take advice from Karl Rove, the former Bush political adviser who recently said some of Perry's rhetoric has been too provocative for a general election.
"Karl has been over the top for a long time now," he said. Backstage, Romney and Perry exchanged small talk, but when they were introduced on stage, they stood stiffly side by side.
Romney, slightly taller and just an arm's length away for the debate, frequently turned his body toward Perry when the Texas governor spoke, watching him intently.
When Romney talked about rebuilding the Massachusetts economy, Perry looked toward the audience with a broadly arched eyebrow.
Despite their clashes, Romney defended Perry from criticism from other contenders who said he had infringed on parents' rights when he tried to require young girls to be vaccinated for sexually transmitted diseases and some cancers. Romney said he had disagreed with Perry's methods but that the Texas governor's heart was in the right place - then sought to move the conversation away from social issues and back to job creation.
The event was Perry's first opportunity to share a debate stage with his rivals since he joined the race last month and shot to the top of the public opinion polls. He displaced Romney as front-runner and stepped on the momentum that Bachmann had generated with her victory in a straw poll at the Iowa State Fair earlier in the summer.
A governor for more than a decade, he seemed at ease on stage in his campaign debut and moved quickly to assert his claim to having the best record of all on stage in creating jobs.
"We created 1 million jobs in the state of Texas at the same time the United States lost 2 million," he said, adding that the issue for the nation this election season is "who on this stage can get America working. Because we know for a fact that the resident of the White House cannot."
Romney threw the first jab of the evening, saying that being a career politician is a "fine profession" but not the same as having worked in the business world, as he did.
That was a reference to Perry, who moved quickly to counter. He said Romney had indeed done well creating jobs in the business world, but "when he moved that experience to government, he had one of the lowest job creation rates in the country. ... As a matter of fact, we created more jobs in the last three months in Texas than he created in four years in Massachusetts."
Romney didn't exactly challenge that claim, but instead said Texas has no income tax, has a right-to-work law that makes it hard for unions to organize, plentiful oil and gas reserves and a Republican legislature. Massachusetts has none of those things, and he said he had turned the state's economy around.
Associated Press writer Michael R. Blood contributed to this story.