A Guardian/ICM poll gave Clegg a narrow win, with the Lib Dem leader on 33 per cent and Cameron and Brown on 29 per cent each.
Other instant polls have suggested that Cameron narrowly won after the second debate. Taken overall, the polls amounted to almost a dead heat.
Brown failed to top any poll despite a general feeling that his performance was improved.
Labour-leaning Wolfstar MD Stuart Bruce said the debate was 'far more robust' and that all three candidates upped their game.
He said that Brown 'appeared well rehearsed and came across as the most Statesmanlike'. He added: 'Brown wasn't asking you to like him, he just demonstrated that it's a big job that needs a leader of substance. Clegg showed he has what it takes to win the X Factor, but it's Brown who'd win Mastermind.'
Lib Dem-supporting Mandate Communications head of digital Mark Pack said: 'The debate and the post-debate polls have confirmed how the first TV debate has overturned the usual two-party political and media dynamics of UK election campaigns. For Nick Clegg and his party that's a dramatic achievement.'
Shout Communications director Catherine Bayfield said of Cameron's performance: 'Where Mr Cameron excelled was as master of the perfect soundbite. No stutters or ums for the Tory leader, he strings together his sentences slickly and smoothly, not too long, not too short. This is great for news, but in an hour and a half of programming it can't cover up for lack of substance.'
Former Downing Street director of comms Alastair Campbell was quoted as saying: 'I don't care what your polls say. When it comes to substance, real substance, there was only one person out there and that was Gordon Brown.'
In the debate, Brown said of his style: 'If it is all about style and PR, count me out.'
This newspapers' interpretations of the second debate differed wildly.
Tory-leaning newspaper The Daily Telegraph headlined that 'Cameron Fights Back', while The Sun dubbed Cameron 'The Cam Back Kid'.
However, Labour-supporting the Daily Mirror stated: 'David Cameron was on the ropes last night after he again trailed in third in the party leaders' debate.'
The Times led with the more measured 'Neck and Neck'. Only The Guardian made reference to the Lib Dem leader with the headline 'Clegg Survives the Storm'.
The second leaders' debate had a live audience of 4 million viewers across Sky News, BBC News Channel and Sky3 last night.
The televised encounter attracted 2.125 million viewers, an 8.7 percent audience share, between 8pm and 9.30pm on Sky News.