The Tea Party is poised for another come-from-behind victory Tuesday, when its U.S. Senate candidate in Texas, Republican Ted Cruz, is expected to beat his better-financed, establishment-backed GOP opponent by as much as 10 percentage points in a runoff race.

"We have named tomorrow Cruz Day, instead of Tuesday," Katrina Pierson, a jubilant Texas Tea Party volunteer, told The Washington Examiner on the eve of Cruz's showdown with Lt. Gov. David Dewhurst.

Cruz and Dewhurst were the top finishers in the May 29 Republican Senate primary, when Dewhurst topped Cruz by 10 percentage points. But with an intense grassroots effort combined with outside money from so-called super PACs, Cruz has reversed those numbers.

"This entire campaign has been a tremendous testament to the power of the conservative grassroots," Cruz told The Examiner. "When we started the campaign a year-and-a-half ago, I was at 2 percent in the polls. There wasn't a soul in Texas who gave us a prayer."

Dewhurst, who did not respond to a request for an interview, now trails Cruz, despite endorsements from Gov. Rick Perry, Republican state legislators and a campaign that outspent Cruz 4-to-1.

"If Cruz wins, it will provide another example of a very interesting strategy of combining grassroots with external money, which allows you to compete against the establishment in your state," said Mark Jones, a political science professor at Rice University in Houston.

Tea Party activists employed a similar tactic to help oust Sen. Richard Lugar, a longtime Republican incumbent in Indiana in May and again a month later to rescue Republican Gov. Scott Walker of Wisconsin from a recall election.

It's a strategy the Tea Party has been using since it burst onto the scene in 2010 and, among other victories, cleared the way to U.S. Senate seats for Mike Lee in Utah and Marco Rubio in Florida.

"We successfully nationalized, like we did for Rubio, Lee, Scott Walker," said Brendan Steinhauser, the federal and state campaigns director for FreedomWorks, a Tea Party super PAC pumping millions into Cruz's primary and runoff efforts.

"We were able to get people from over 40 states to make calls for Cruz," Steinhauser added. "He got money from 35,000 individual donors."

While Dewhurst had the backing of Texas conservatives, Cruz was aided by national Tea Party stars like former Alaska Gov. Sarah Palin and Sen. Jim DeMint, R-S.C., as well as popular conservative radio hosts Mark Levin and Sean Hannity.

Dewhurst tried to turn Cruz's out-of-state support into evidence that Cruz was an outsider, but Steinhauser, a Texas native, said those effort largely backfired.

"Texas conservatives love these guys," Steinhauser said of the national luminaries. "Tea Partiers band together state to state. There's no backlash because it's a national fight."

Dewhurst may also have been damaged by the endorsement of Perry, whose popularity plummeted since his gaffe-filled, ill-fated presidential run. The only silver lining for Dewhurst is that he's leading among seniors, largely because Cruz ignored those voters.

"We are just mainly focused on the 65-and-under crowd," said Pierson. "That is where the energy is coming from, where people are engaged."

The winner of Tuesday's Republican runoff will likely be the next U.S. senator from Texas, since no Democrat has won a statewide election since 1994.