Christine O'Donnell, the populist Tea Party favourite, has received more than $1m (£640,000) in donations since her surprise win in Delaware on Tuesday, despite her ultra-conservative social views, it emerged today.

Rightwingers from across the US have poured funds into her campaign, and the Republican national senatorial campaign committee, which initially said it would not give her any financial support for her campaign against the Democrats for the seat in November, today caved in to angry calls from her supporters and said it was sending her a cheque for $42,000.

In one of the unlikeliest upsets of the year, O'Donnell won a contest to fight the US Senate seat in Delaware for the Republicans after beating the party establishment favourite, Mike Castle.

Her views on evolution, sexual purity and medical research have made her a figure of ridicule in the US media, as have her chaotic personal finances.

Today new details emerged of an interview with Fox's Bill O'Reilly in November 2007 in which she made the claim, without any foundation, that: "American scientific companies are cross-breeding humans and animals and coming up with mice with fully functioning human brains."

But grassroots supporters, many who regard the media as liberal and biased, see her as a welcome change from men in suits. O'Donnell's spokeswoman, Michelle Lauren, said the campaign's website had crashed on Tuesday night because of the volume of traffic generated by her win. Her campaign, which had until then been run on a shoestring, raised $850,000 in the first 24 hours, Lauren said.

Her victory has highlighted the extent of the civil war being waged inside the Republican party between the Washington-based establishment and populist movements such as the Tea Party.

The Republican party chairman in Delaware, Tom Ross, who had said before her win that she was incapable of being elected a dog-catcher, today issued a statement saying it was time for the party to unite behind her.

In contrast with the lukewarm support at national level, a Republican senator on the right of the party, Jim DeMint, who had backed her against the party establishment, said his office had been inundated with donations for her and raised $174,000 in the first 48 hours after her win.

Although O'Donnell won the Republican nomination, there are doubts about whether she can take the Senate seat from the Democrats, given that Delaware is one of the most Democratic states in the US. But it is also a small state and the amount of money being channelled to her will make a big impact, especially as the state is not used to the kind of saturation political advertising such funding will provide.

"Despite what some Beltway pundits think, Americans clearly believe that Christine can and should win it," DeMint said in a statement.

In contrast with the funding O'Donnell achieved in the first 24 hours, her Democratic opponent, Chris Coons, took in only $125,000. While the poll gap between the Republicans and Democrats in the state remains huge, her win created sufficient alarm for the vice-president, Joe Biden, who held the Senate seat until 2008, to visit the state today to support Coons.

O'Donnell was today preparing to use the money to expand her small election team. Her campaign website was also cleaned, possibly to remove any comments that might embarrass her in the election. In spite of that, US journalists were unearthing all sorts of awkward quotes.

Karl Rove, George Bush's political strategist, who heavily criticised O'Donnell on Tuesday night, saying she could cost the Republicans any chance of winning Delaware, retreated today and threw his support behind her.

After a series of Tea Party rallies in Washington, including one last month headlined by Sarah Palin and the conservative commentator Glenn Beck, the comedians Jon Stewart and Stephen Colbert announced on their shows on Thursday night they are to organise a counter-rally in Washington on 30 October. Stewart dubbed it A March for Sanity.