Ashley Giles wants to see England's 'A' game against Australia

England one-day coach Ashley Giles wants to see the side produce their "A game" in their Champions Trophy opener at Edgbaston on Saturday.

Tournament hosts England were below their best for much of their recent 2-1 one-day series defeat by New Zealand, although they did at least avoid a whitewash with a 34-run win over the Black Caps in Nottingham on Wednesday.

England's bowling attack wasn't helped in the first two matches by being without seamers Stuart Broad (knee) and Steven Finn (shin), both of whom returned to action without any obvious ill-effects on Wednesday.

But a batting line-up without Kevin Pietersen, who will miss the Champions Trophy as he continues a recovery from a knee injury that England hope will heal by the time they begin the defence of the Ashes next month, lacked dash for much of the series.

And but for Jos Buttler's breathtaking 47 not out off just 16 balls on Wednesday, England might have suffered yet another defeat.

"I'm certainly buoyed from this match (at Trent Bridge), because it was much better," said former England left-arm spinner Giles, an Ashes winner in 2005.

"It was still not anywhere near a perfect performance. It's disappointing to have lost a series, and we've let ourselves down in certain departments.

"There are some big positives, but we've certainly not played our 'A' game yet.

"Maybe we're saving that."

Wicketkeeper-batsman Buttler, still only 22, produced an array of astonishing shots on Wednesday, with the Somerset starlet seemingly uninhibited despite not even taking guard until the 47th over.

Giles, who will be on familiar territory on Saturday, having both played and coached Edgbaston-based county Warwickshire, believes Buttler is capable of more than mere 'cameo' innings.

"I think he can do it over a longer period," Giles said. "I think what Jos needed was to do it once in 50-over cricket. It doesn't mean he's going to do it all the time - but in Twenty20 cricket, once he crossed that hurdle, he looked a different player.

"I'm hoping that will happen again."

But the fact that Buttler came to the crease after Ravi Bopara and Eoin Morgan had performed something of a rebuilding job, left Giles thinking it might be best just to leave him at number seven rather than move him up the order.

"I think the batting order, playing an extra batter in Ravi, might have given him a bit more confidence -- it takes a little bit of pressure off him and gives him a bit more freedom," Giles explained.

"It doesn't necessarily mean that's the way we're going to go. But Jos has shown in Twenty20 cricket he is built for coming in for five overs.

"Cooky (England captain Alastair Cook) and I sat and the balcony and said '30 off 10 balls would be nice'. He (Buttler) exceeded all our expectations, so I'm really chuffed for him."