"When I was considering running and down 30 points, the only person that actually met me was Senator McCain," Brown said at a McCain rally Saturday.
McCain's early support helped Brown, a better known, better funded Democrat in liberal-leaning Massachusetts.
Now McCain is enlisting the GOP's newest superstar to help him with his own election, a Senate primary challenge from the right.
J.D. Hayworth, conservative radio host and former congressman, is hoping to corral the Tea Party crowd and.
"Everything that the McCain people tried to do to intimidate me not to run has just moved me in the other direction," Hayworth said on a radio show.
Hayworth's challenge has forced McCain to tack to the right recently, saying while standing next to Brown at the rally, "We don't want terrorists read their Miranda rights."
McCain's also dusted off his outsider credentials with visits from Tea Party idols like former Alaska Gov. Sarah Palin and Brown, who McCain called "one of the great political heroes in American political history."
With polls showing anti-Washington anger at an all-time high, McCain is one of many incumbents facing tough elections.
Senate Majority Leader Harry Reid, Arkansas Sen. and Pennsylvania Sen. - all Democrats - are all enduring bruising campaign battles. Several more senators have retired to avoid the anti-incumbent environment.
"You've got long-term senators who have locked down election after election - and won by 10, 20 points every time - who are scared out of their minds," said Politico's Andy Barr.
It's unfamiliar territory for McCain, who cruised to victory in Arizona in 2004 with 76 percent of the vote. Arizona's Tea Party hasn't endorsed McCain or Hayworth, saying that from the group's perspective both of their records leave a lot to be desired.