David Cameron warned voters that anything but a "decisive" Tory victory on May 6 would leave Labour in charge as he sought to fight off a surge in public support for the Liberal Democrats.
The Conservative leader declined to follow Gordon Brown in admitting he had "lost" to Lib Dem leader Nick Clegg in the presentation stakes during the first leaders' debate on TV.
He said he was confident he had got his message across on key issues and would continue to run a "positive" campaign despite pressure to attack the third party.
Addressing an audience of mainly older voters, including his own parents, in a pub garden in Swindon, he was asked if he too believed he had lost to Mr Clegg in the debate and that the Lib Dems were now regarded as the party offering "change".
"People will judge the debates, people will decide what matters in these debates. What I think matters the most is getting your case across about the change you want to bring," he said.
"Whether it's the need to control immigration, whether it's the need for a tougher approach on crime, whether it is how we improve our health service, on all of those subjects, people watching at home can hear how the potential leaders of our country actually believe about those things," he said.
Mr Cameron went on: "If you want real change, if you want the job to be done, the only way to get it done is to have a Conservative government.
"If you want to wake up on May 7 and be absolutely certain that you've got new leadership in this country and are not stuck with another five years of Gordon Brown, stuck with dithering and despair and depression, the only way to get that is a decisive Conservative vote.
"My response to all that is happening in this campaign is to accentuate the positive.
"Never mind what the others are doing, let's concentrate on what we are going to bring to this great country."
