Symonds, Ponting and Lee celebrate (Getty Images).

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Ricky Ponting praised zero-turned-hero Andrew Symonds after Australia ensured they will defend their World Cup title with a rain-affected 48-run win over Sri Lanka.

Much criticism surrounded Symonds' inclusion in the 15-man party for this tournament but a clinical, unbeaten 91 at St George's Park was the platform for a 16th consecutive one-day win for the Aussies.

They struggled early in their innings for a third time in Port Elizabeth - England and New Zealand exploited the bowler-friendly conditions - before posting a defendable 212 for seven.

That was largely the work of Kent and Queensland all-rounder Symonds, 27, who struck seven fours and a six in his 118-ball innings.

Brett Lee's pace then ripped through the Sri Lankan top order and they never recovered, reaching 123 for seven when rain washed out the contest in the 39th over.

Having struggled to score a run in the VB Series which preceded the World Cup, Symonds has now piled up 326 runs in South Africa, where he has been dismissed just twice in five innings.

"If you look at Andrew's numbers they are very good but more importantly the way he's gone about his cricket since he was picked on the tour has been positive, he's worked particularly hard on all aspects of his game.

"He is probably more of a thinking cricketer than he was in the past and I couldn't be happier with the way he's gone about things," said Ponting, whose team will face either India or Kenya in Johannesburg on Sunday.

Ponting added that he always wanted the Birmingham-born player - who turned down a chance to play for England in 1995 - in his World Cup 15 despite accusations he had never performed at the top level.

"It was down to the last few positions in the touring party and I just got my point across to the selectors that I thought Andrew would be a very good inclusion in our squad," Ponting added.

"I knew what he was capable of and he's almost won us a couple of games off his own back."

The first of those performances, his maiden one-day international century, 143 not out against Pakistan at the Wanderers, turned the tide for Symonds.

"Practice has made a big difference and I have had a lot of assistance from the team," Symonds said.

"After the first game my confidence was as high as it has ever been."

Using his experience of previous strips at St George's Park in this tournament, Ponting believed Australia had enough when they beat their previous score of 208.

"We knew the if we bowled well with the new ball it would be vital and once we got those early wickets," said Ponting.

Opposing captain Sanath Jayasuriya was one of four wickets to fall in the first 12 overs and admitted consolidating would have been crucial.

"What we wanted to do was occupy the crease for the first 10 overs and if we had done that we would have handled Brett Lee," he said. "If we hadn't lost so many wickets we would have done something better."

All hope had gone when Aravinda de Silva, who confirmed his retirement from international cricket after the defeat, was brilliantly run out by Andy Bichel.

"I was hoping that this wasn't my last one," said de Silva, 37, a World Cup winner with Sri Lanka in 1996.

"But unfortunately it has been an emotional day for me; it was pretty sad that after doing the hard work we didn't apply ourselves when we batted.

"We should have gone on and won, I thought that was a very good total for us to chase."

His finale contained one of the stranger instances of the modern game when Australian opener Adam Gilchrist walked after inside-edging a catch to Kumar Sangakkara off de Silva's bowling despite umpire Rudi Koertzen saying 'not out'.

"It was a good gesture on Gilchrist's part to have walked off," reflected de Silva. "It's very rare nowadays to see a batsman walking off; Brian Lara does it all the time and there are some gentlemen left still."

Ponting explained: "Talking to Gilchrist, he said he didn't hear Rudi Koertzen say 'not out'. He knew he got a bit of bat on it and didn't bother looking around at the umpire.

"I won't be encouraging any of our batsmen to walk, it is up to them whether they do or not, however they see it on the day."