Palin, among the most popular figures with those activists, appeared with McCain for the first time since the pair lost the 2008 presidential election.
"Everyone here supporting John McCain, we are all part of that tea party movement," Palin told the rally.
As the former Alaska governor and McCain took the stage, the crowd chanted, "Sarah, Sarah," not the name of the man who just a year and a half ago topped his party's ticket.
Palin said McCain warned the country that Obama's policies would increase the size of government and the debt, and that the signing this week of a health overhaul law proves McCain right.
She took heat this week when she released a list of 20 U.S. House seats she said conservatives should try to win in the November elections. The list, posted on her Facebook page, featured a U.S. map with circles and cross hairs over the 20 districts. She also sent a tweet saying, "Don't Retreat, Instead - RELOAD!" Critics said it was inappropriate to use gun imagery, especially as some Democrats who supported the health care overhaul reported receiving threats of violence.
Palin called it a "ginned up" controversy and defended her rhetoric.
"When we take up our arms, we're talking about our vote," she said.
Palin said the Republican Party needs new blood and new leaders, "but we also need statesmen and heroes like John McCain in there to help us get through these challenging times."
Hayworth has tried to define himself as "the consistent conservative" in contrast to the "maverick" McCain.
Before Hayworth left his radio show to enter the race, he used the airwaves to attack McCain's congressional record, most notably his work with the late Sen. Edward M. Kennedy on a bill that would have created a pathway to citizenship for illegal immigrants.
Hayworth supporters outside McCain's rally Friday were unimpressed with Palin's support for the senator, saying she is helping him because McCain launched her national political career by making her his vice presidential pick.
"It's disappointing, but a lot of us understand it's just political payback," said Jennifer Leslie, 41, of Oro Valley, Ariz. McCain is "calling in his favors."
Leslie carried a sign that said "Sarah supporter for JD Hayworth" and wrote "JD" on her hand.