(CNN) -- TV commentator and Tea Party favorite Christine O'Donnell defeated U.S. Rep. Mike Castle in Delaware's Republican U.S. Senate primary Tuesday.
O'Donnell won more than 53 percent of the vote in the bitter campaign that displayed internal Republican warfare.
O'Donnell on Tuesday night thanked her supporters, including Tea Party groups, saying they "rallied everyday Americans outside of the political establishment, [got] them involved and created a grassroots network that made all of this possible."
"Don't ever underestimate the power of we, the people," O'Donnell said to raucous cheers from her supporters. "We, the people, will have our voice heard in Washington, D.C., once again."
Castle, a former Delaware governor who has served nine terms in the House, thanked supporters in a concession speech Tuesday night.
"The last several weeks have been spirited, shall we say, and the voters of the Republican primary have spoken, and I respect that decision," Castle said.
In the closing days of the primary campaign, O'Donnell got a boost with an endorsement by former Alaska Gov. Sarah Palin and more than $150,000 in late contributions from the Tea Party Express.
The GOP establishment is concerned O'Donnell has no chance of winning the seat -- once held by Joe Biden for 26 years before he became vice president -- in November. A top Republican official warned Tuesday night that national Republicans will be slow to rally around O'Donnell.
"Until she demonstrates some viability in the polls, we are not going to have any money for her," the official told CNN. "It is now incumbent on Sarah Palin, [U.S. Sen.] Jim DeMint [of South Carolina] and the Tea Party Express to help support her. They got her here. Now make it happen."
O'Donnell told CNN's Jessica Yellin on Tuesday night that she'd "love [establishment Republicans'] support, but they're the same so-called experts who said I couldn't win the primary."
"If we just had that throw-in-the towel mentality every time there was a fight that needed to be fought, our country wouldn't be what it is," O'Donnell said.
"There's a lot of visionaries and leaders ... in this room who believe we can win, and if [establishment Republicans are] too lazy to put in the effort that we need to win, then so be it. We're going to win without them. I'd love their support, but we're going to win without them."
O'Donnell positioned herself as a conservative gate-crasher.
"We're breaking up the backroom deals," she told CNN before Tuesday's primary. "We're restoring the political process back to the hands of the people." She refers to Castle as the "anointed one."
In an interview before the primary, O'Donnell told CNN:
-- The Republican Party is behind "false accusations and attack ads" against her and accused party operatives of "fighting for not only my opponent's political career but their own political career."
-- She believes it's "a shame" that FreedomWorks, the Dick Armey group that backs Tea Party candidates, declined to endorse her but disagrees with the organization's view that she can't win the general election, saying, "No one even thought we could get this far."
-- Palin's endorsement "is helping a lot" because "it gave my supporters an extra boost of encouragement." And it helped her, too: "Gov. Palin can relate to the politics of personal destruction, and she's survived them and they didn't get her down."
-- And she says she'd love support from one well-known Democrat: "I would love Hillary Clinton's endorsement. When I saw her presidential ads, I said, 'You go, girl!' I'm a Republican, so I probably won't vote for her, but I do admire her."
Democrats were positively gleeful at the prospect of an O'Donnell victory on Tuesday. Many had written off Vice President Joe Biden's old Senate seat as a loss. But with O'Donnell the projected winner, Democrats believe they can hold the seat in November, which could save their majority in the Senate.
The big unknown heading into Tuesday was voter turnout. There are fewer than 183,000 registered Republicans in the state. It's a closed primary -- meaning neither Democrats (about 293,000 registered voters) nor independents (146,000 registered as "other") can vote. And in an off-year primary, few voters tend to turn out.
So this race -- and perhaps the balance of power in the Senate -- was decided by fewer people than usually turn out for a Palin rally.
CNN's Mark Preston contributed to this report