The three leaders were all out campaigning on Friday
Gordon Brown has said he has to "try harder" and "dig deeper" as party leaders return to the campaign trail after the final TV debate.
The PM, who snap polls suggested was seen to come third in the debate, said the TV clashes were over and decision time for voters was beginning.
Tory leader David Cameron said the election was "far from won".
Lib Dem leader Nick Clegg said the election was now a "two-horse race" between his party and the Tories.
In other election developments on Friday:
Snap polls suggested Mr Cameron was seen to do best in the final live debate - watched by 8.4m people on average - peaking at 9.1m at 2100 BST.
'Very last second'
Launching a Labour poster campaign in Hockley in the West Midlands, Mr Brown told supporters: "The time for debates has finished and the time for decision has begun... We will continue to fight for the future of this country until the very last second of this election campaign."
And speaking to students at Loughborough University, he acknowledged he still had to win over voters, as the election campaign enters its final phase.
After quoting Scottish Olympic athlete Eric Liddell he said: "You've got to have this inner reservoir of determination and resilience to fight back when anything happens to you. It's a pretty good motto to try harder, to work longer and to dig deeper - that's what I've got to do over the next few days."
Mr Brown had been under pressure to get Labour's campaign back on track after he had to apologise on Wednesday to a pensioner he was unwittingly recorded calling "bigoted" after she raised concerns over immigration with him.
Visiting a health clinic in Harrow, his predecessor Mr Blair said it was a "tough job being prime minister, I know" and told reporters Labour "has every chance of succeeding".
Chancellor Alistair Darling has also spoken about the Labour leadership, telling the BBC he has "absolutely no ambition" in becoming an interim leader should Mr Brown stand down after the general election - if Labour were to lose.
He also confirmed that the prime minister had asked him to remain as chancellor should Labour win on 6 May.
On the campaign trail in Derby, Mr Cameron said: "This election is far from over, we are now entering the most energetic and most important stage of this campaign which is getting to every part of the country and convincing people if you want change to happen... then it's the Conservatives that can deliver that."
He said there were "millions of people still making up their minds" about how to vote and he wanted to persuade them to back his party. Asked about Mr Blair's visit, he said: "It's great to have him back in the country. He's one of the few people who can actually afford another Labour government."
Addressing students in Leicester, Mr Clegg did his best to ignore Labour supporters in the crowd as he repeated his promises to clean up politics and bring fairness to tax. He told the BBC his party was "going for gold in getting the most number of people voting for the Liberal Democrats".
He said everyone wanted "change", the question was, what kind of change: "I think this election campaign is now boiling down to a simple choice - a two-horse race between the Conservative Party and the Liberal Democrats."
Late on Friday, the Guardian website published an editorial backing the Lib Dems because of the party's call for reform of the voting system.
Party leaders discussed subjects including economic policy, immigration, housing, political reform, education, tax, banking reform and spending cuts during the 90-minute debate hosted by the BBC's David Dimbleby in Birmingham.
Instant polls published after the debate suggested viewers felt Mr Cameron did best. A YouGov poll for The Sun found 41% of people saying the Tory leader performed best compared to 32% for Nick Clegg and 25% for Gordon Brown. A ComRes poll for ITV News put Mr Cameron on 35%, Mr Clegg on 33% and Mr Brown on 26%.
BBC polling expert David Cowling said they showed exactly the same movement - no change for Mr Clegg over the second debate, an increase of 5% for Mr Cameron and a drop of 4% for Mr Brown.
Giving his reaction to the encounter, Scottish National Party leader Alex Salmond said: "I don't think there was any clear winner. Gordon Brown was certainly the loser - just in terms of his demeanour through the debate." The SNP failed in its legal action to try to block the broadcast in Scotland unless it featured Mr Salmond.
Plaid Cymru leader Ieuan Wyn Jones said: "What I didn't hear tonight was any of them recognising the special problems that we have particularly here in Wales."
• Jeremy Paxman will interview Gordon Brown at 2030 BST on BBC One.