Nigel Farage emerged on top after a bitter face-off with Nick Clegg which saw them brand each other liars and fantasists, according to a poll.
A snap YouGov survey suggested 68% thought the Ukip leader had performed best in their second televised debate, compared to 27% who favoured the Deputy Prime Minister.
The verdict followed an hour of increasingly bad-tempered exchanges, with Mr Clegg repeatedly accusing his opponent of "fantasy".
He also picked up Mr Farage for "indefensible" comments in which he suggested he admired Russian president Vladimir Putin for outwitting the EU and western leaders.
"I wouldn't be surprised if Nigel Farage soon tells us that the moon landing was a fake, that Barack Obama is not American, that Elvis is not dead," Mr Clegg said.
But Mr Farage retorted that the Liberal Democrat leader was "wilfully lying" about how many laws were imposed on the UK by the EU.
"I said yes to these debates. I thought you would honestly make the pro-EU case," Mr Farage said. "By saying 7% of our laws are made in Brussels, you are wilfully lying to the British people about the extent to which we have given away control of our country and our democracy and I'm really shocked and surprised that you would try and do that."
During one of the hardest-fought passages, Mr Farage warned that immigration had been a "disaster" and left the "white working-class effectively as an underclass".
A separate Guardian/ICM poll also gave Mr Farage victory, by 69% to 31%.
The margin was larger than the 57% to 36% recorded by YouGov in an equivalent snap survey last Wednesday.
Mr Clegg took a more aggressive and impassioned approach to get his message across and unsettle Mr Farage.
The Ukip leader said the scale of immigration over recent years had "shocked" the country and increased segregation in towns and cities.
"Worst of all what it has done socially, it has left, I'm afraid, the white working class - and yes, I know educationally many of them have not done as well as we would have liked - but it has left the white working class effectively as an underclass, and I think that is a disaster for our society," Mr Farage said.
But Mr Clegg insisted there were "always problems when you have people".
"The idea that there will be no problems at all where we are not part of the EU... you can't simply wish away the fact that people down the centuries have moved from one country to the next.
"What we need to make sure is that people play by the rules, they don't exploit our generosity through benefits, we make sure we support public services and we make sure we support jobs in our country that go to many British people."
Mr Clegg said it was "silly" to suggest that 485 million people in Europe were about to come to Britain.
"It is as silly as me saying that five million people living in Scotland might all move to Orpington next Tuesday. It is not going to happen."
Mr Farage said immigration had benefited "rich people" by suppressing the costs of their staff and services.
"It is good for the rich because it is cheaper nannies and cheaper chauffeurs and cheaper gardeners," he said. "But it is bad news for ordinary Britons. We need to have a control on immigration, on the numbers who come here and over the quality who come here."
Warning of a further wave of immigration from countries such as Greece and Spain, Mr Farage accused the Deputy Prime Minister of being part of a "career political class" who were in cahoots with big business and wanted to maintain the status quo.
However, Mr Clegg warned the audience not to buy Mr Farage's argument that Britain could have all the positives of EU membership without any of the costs. At one point he accused the Ukip leader of "making things up to make a point".
"I f it sounds too good to be true then it probably is," he said.
"It is a dangerous con, because the modern world has changed. Our economies are intertwined with each other ."
Mr Clegg condemned a Ukip leaflet depicting a native American Indian and suggesting they had ignored immigration and now "lived on a reservation". Mr Farage said he "did not recognise" the document and did not "endorse the sentiments".
The Lib Dem leader lambasted his opponent for expressing admiration for Mr Putin, saying it demonstrated how dogmatic his attitude was that he supported the Russian premier over the EU.
Mr Clegg said Mr Farage had treated the suffering of millions of Syrians at the hands of Bashar Assad's brutal regime like a game.
"This isn't some sort of pub bar discussion, this is a serious issue about how we stop the slaughter, the displacement of millions of people, women and children being sexually abused, terrible violence on an unimaginable scale and all Nigel Farage can say is that he (Mr Putin) has played it brilliantly," he said.
But Mr Farage said the crisis in Ukraine had been caused by the overthrow of the "democratically elected" Russian-facing president Victor Yanukovych.
"If you look at what's happened with the Ukraine we've had a message that's been sent out for 10 years, and this is not just the EU, David Cameron, Nick Clegg, and I'm afraid and Ed Miliband too, have all been saying to the Ukraine 'look, why don't you come and join the European Union? While you are at it, why don't you join Nato too?'" he said.
"And this is something that has been seen by Putin to be a deeply provocative act. We have given false hope to those western Ukrainians. And did you see them with their EU flags and their banners?
"They actually toppled a democratically elected leader. Yes, I know Ukraine's corrupt, I know it wasn't perfect, but they toppled a leader and I do not want to be part of an emerging, expansionist EU foreign policy. I think it will be a danger to peace."
Turning to Syria, Mr Farage said: "I think if Putin had not pointed out that the use of Sarin gas had not necessarily come from the Assad regime, if he hadn't done that, I suspect the backbench rebels would not have defeated you Nick in stopping us from going to war."
He went on: "This country, Nick, has had enough of getting involved in dangerous foreign wars.
"There is no evidence that our military intervention in these countries is making things better.
"With you as Deputy Prime Minister we bombed Libya and it is worse now than it was then."
In his final appeal to viewers, Mr Farage said: "I would urge people; come and join the people's army, let's topple the establishment who have led us to this mess."
But Mr Clegg said Ukip was harking back to a 19th century ideal when "Britain had the empire, women knew their place and stayed at home, people who are gay were not allowed to get married".
He said those defending Britain's links with Europe were offering "real remedies for the way that the world is today, not dangerous fantasies about a bygone world that no longer exists".