The Tory leader targeted Mr Balls directly as he visited the newly created seat being fought by Prime Minister Gordon Brown’s closest political ally.
Party strategists believe the slump in Labour opinion poll support has put constituencies like Morley and Outwood, in West Yorkshire, within their reach despite needing a 10.47% swing to reverse a notional 8,669 majority.
Such a prized scalp on election night could prove as symbolic as the unexpected defeat of Tory cabinet minister Michael Portillo in 1997 – probably the most memorable moment of that election.
“We’d all love a Portillo moment, but that’s up to the voters,” he said as he spoke to staff in the Coca Cola bottling plant in Outwood, near Wakefield.
Appearing alongside the Tory candidate, Antony Calvert, he denied the focus on Labour-held seats meant he had abandoned efforts in Liberal Democrat-held marginals after they enjoyed a surge in popular support.
“You can see that the Labour campaign’s in difficulty. Antony’s fighting a great campaign. I want to be here to support him so we can try and win this seat... but I haven’t given up in Lib Dem seats.”
Mr Cameron also delivered a personal broadside against the Labour cabinet minister’s private education – accusing him of hiding his schooling while labelling the Eton-educated Tory leader a “toff”.
“Ed Balls and I have one thing in common which is we both went to a private independent school. The difference is I don’t hide it. I have never hidden my background or my family or where I am from.”
He added: “It doesn’t matter where you come from, we should be building a country where it doesn’t matter where you come from. You can rise according to your talent and your ability.”
Ahead of tonight’s final televised leaders’ debate – which will centre on the economy – Mr Cameron insisted the party had gone as far as it could in setting out where it could cut spending after the election.
The Institute for Fiscal Studies accused all three main parties yesterday of failing to come clean over the scale of the public spending cuts needed after the May 6 poll.
Conservative plans involved larger spending reductions than in any five-year period since the Second World War, said the think tank, but only a fifth of the detail had been made public.
“I think we have gone further and faster than any opposition in British political history in saying here are tough things that need to be done and also we have said we accept that is still not enough,” he said.
“We are going to have to freeze public sector pay, we are going to have to ask people to retire a year later, we are going to have to say to people on over £50,000 you can’t go on having tax credits. Those are tough and difficult things.
“As an opposition, when we have got a Government which hasn’t even done a three-year spending review, is there more we could do?
“I don’t think there is.”