Pietersen, whose 104 was England's first century this World Cup, put on 140 for the third wicket with Ian Bell (77) after his side slumped to 24 for two.
But Australia fought back by taking three wickets for 15 runs in six overs as England declined from 164 for two to 179 for five.
Ravi Bopara, who almost saw England to victory in Wednesday's two-run defeat against Sri Lanka, chipped in with 21 in a stand of 51 with Pietersen.
Left-arm quick Nathan Bracken had an economical three for 33, fast bowler Shaun Tait three for 41 and Glenn McGrath, in what could be his last match against England before retirement, three for 62.
Just 51 runs came in the last 10 overs with Pietersen, whose fourth century at this level came off 117 balls with one six and six fours, scoring just one boundary between fifty and a hundred when he was dropped twice
Although England didn't have to win to keep their semi-final hopes alive, defeat would lead them needing to win all three of their remaining Super Eights matches against Bangladesh, South Africa and the West Indies while hoping other results went their way.
Against an Australia side unbeaten in the tournament so far, England saw skipper Michael Vaughan (five) and Andrew Strauss, normally an opener but batting at three after Middlesex team-mate Ed Joyce was dropped, both play on to Tait.
Vaughan's early exit after winning the toss meant he'd now scored just 83 runs from six tournament innings.
Pietersen, who had his tour of Australia ended when McGrath broke his rib in Melbourne in January, advanced down the pitch and whipped him through mid-wicket in trademark style.
Bell was especially severe on McGrath, hitting him for three fours in his third over, the best a front-foot drive through mid-off.
McGrath saw his first three overs cost 25 runs.
Australia captain Ricky Ponting, without injured pace bowling all-rounder Shane Watson, brought on part-time left-arm spinner Michael Clarke whom Pietersen lofted for a four and six over long-on off successive balls.
Andrew Symonds, fit to bowl medium-pace after a biceps problem, saw his six overs cost 40 runs.
The South Africa-born Pietersen, still on 50, had a reprieve when after driving a Symonds full toss, he saw a diving Ponting at mid-on drop what would have been a superb one-handed catch.
He had another slice of luck when, on 63, he miscued a drive off Tait only for Matthew Hayden, coming round from mid-off, to drop the seemingly simple chance despite getting two hands to the ball.
Australia, beaten 2-0 at home in England in the CB series finals before a five-wicket warm-up win in St Vincent last month, then regained control.
Bell drove McGrath straight to Michael Hussey at cover to end a 90-ball innings with nine fours and Paul Collingwood (two) was caught behind off Tait.
Andrew Flintoff's wretched time with the bat continued when, stranded on one knee, he misread left-arm wrist spinner Brad Hogg and was stumped by Adam Gilchrist for four.
England, as happened against Sri Lanka, had seen a promising position disappear rapidly.
Pietersen fell in the penultimate over when he holed out against Bracken to Clarke at long-off.
England 247 all out in 49.5 overs (Kevin Pietersen 104, Ian Bell 77, Ravinder Bopara 21; Bracken 3 for 33, Tait 3 for 41, McGrath 3 for 62) Vs Australia (yet to bat).