England was 234 for five in their second innings, a lead of 202 runs, with Bell 105 not out and nightwatchman Tim Bresnan unbeaten on four. 
They'd been in dire straits at 49 for three when Bell, who earlier in his Test career was criticised for not making runs when they were most needed, came to the crease following a treble strike by fast bowler Ryan Harris. 
But a fourth-wicket partnership of 106 between Bell and Kevin Pietersen (44) checked Australia's advance. Bell then added 66 with Jonny Bairstow (28) before the Yorkshireman was out shortly before stumps, caught behind off spinner Nathan Lyon.
Having twice made 109 in England's victories at Trent Bridge and Lord's that left them 2-0 up ahead of the drawn third Test at Old Trafford that saw his side retain the Ashes,
Bell's latest century gave the hosts hope of securing a win in this match that would see them take the five-match series outright.
"We needed someone to go out there and get some runs, and that's what I managed to do," Bell, only the third England batsman to score three hundreds in a home Ashes series after Maurice Leyland (1934) and David Gower (1985), told Sky Sports.
"Now we want to go out there on Monday and do the same. We've got to try and get as many as we can and then we've got 10 wickets to get. I'm sure the pitch will deteriorate on the fourth and fifth days," the 31-year-old Warwickshire right-hander added.
Harris took three England top-order wickets for 18 runs in 24 balls. He first bowled Joe Root (two) with a superb seaming delivery that clipped the top of off stump.
And, with conditions still overcast, he had England captain Alastair Cook, on 22, nicking a loose drive to wicketkeeper Brad Haddin. Jonathan Trott then gloved Harris and was well caught down the legside by a leaping Haddin for 23.
Bell though late cut Peter Siddle for four and played an even finer variant of the same shot, also for a boundary, against all-rounder Shane Watson. Pietersen ended the second session by cutting Siddle for four to leave England 123 for three at tea, with both their fourth-wicket batsmen 37 not out.
Australia found themselves a bowler down when Watson went off midway through his seventh over with a right hip/groin injury. Lyon though had Pietersen caught off a leading edge by Chris Rogers at short extra-cover.
England were now 155 for four - a lead of 123 runs - but Bairstow kept Australia at bay for more than an hour.


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