England's tour Down Under took a devastating turn for the worst today when star batsman Kevin Pietersen was forced to return home with a broken rib.

The Hampshire ace walked into a short ball from Glenn McGrath late on in his innings of 82 as England went down by eight wickets to Australia at the MCG in the opening match of the Commonwealth Bank Series.

Although Pietersen, who was on 73 at the time, grimaced on for a handful of overs, the bruise revealed on the right side of his ribcage when physio Dean Conway lifted his shirt suggested serious damage.

Scans at a local hospital confirmed the fracture and the medical assessment suggests he will be out of action for between three and five weeks.

Pietersen, 26, was the one genuine success of the Ashes whitewash, scoring 490 runs, and has been the one-day team's most productive batsman since making his debut two years ago.

England, who will now have to prepare for the World Cup without the world's number-two ranked one-day batsman, are set to name a replacement within 24 hours.

Pietersen will return to the UK in the next couple of days and begin his recuperation ahead of the trip to the Caribbean on March 2.

England went into the triangular tournament intent on improving an atrocious run of just six wins from their previous 25 one-day internationals against Test-class opposition.

But Adam Gilchrist's latest assault put their 242-8 into context.

Gilchrist blasted 60 off only 61 balls as Australia's openers put on 101 in 15 overs.

Both Gilchrist and first-wicket partner Matthew Hayden fell to spin in quick succession but Aussie captain Ricky Ponting and Michael Clarke showed their class to get the hosts home with 28 balls to spare.

The most impressive shot of the pursuit came in the 12th over as Gilchrist took a delivery from outside off-stump and deposited it into the stands at long-on.

Earlier, Pietersen struck the ball cleanly and consistently to hit three sixes off leg-spinner Cameron White.

Clearly in pain, he holed out in the deep to end what otherwise might have been a devastating partnership with Andrew Flintoff (47 not out from 38 deliveries).

Coming to the crease in the 10th over, he lost partner Ian Bell after the drinks break when a loose drive was easily held at mid-off to give Mitchell Johnson a success.

England were fortuitous not to lose Paul Collingwood as three times in his first half-a-dozen runs he might have been run out.

And he was also missed on 21 when White lost the ball in the sun from a big hit to deep square-leg.

England captain Michael Vaughan, playing his first one-day international for 18 months, showed some of his old finesse before becoming one of Nathan Bracken's three victims.

It might have been worse for Vaughan's men in the opening stages but Bell survived first ball when a flashing chance behind flew off wicketkeeper Gilchrist's gloves for four.

England made just one change from the side that played in Sydney on Tuesday night as the triangular tournament got under way.

Opener Strauss' return came in place of Ed Joyce, who received a gash to his head at the end of nets yesterday when struck on the head while bowling.

England were keen to get Liam Plunkett into their XI but he was unavailable for selection after also being struck by a ball yesterday, this time on the ankle.

That meant fast bowlers James Anderson and Jon Lewis kept their places while 36-year-old wicketkeeper Nixon and left-arm spinner Monty Panesar made their one-day international debuts.

Australia, meanwhile, were without fast bowler Brett Lee due to a bout of bronchitis.