The differences in how Stephen Larkham and Berrick Barnes approach the No.10 Test role are subtle and not quite yet defined.

But there are enough variations in how they play for their teammates to make adjustments and be prepared to adapt - which will be imperative during tonight's quarter-final when newcomer Barnes must show the guile of Larkham to ensure Australia survive at least another week in the tournament.

As far as Lote Tuqiri is concerned, the chief difference is that Barnes listens more to the senior players. Larkham trusts his own judgement, understandable considering that he is a 102-Test senior player.

"Berrick's young and a bit more malleable," Tuqiri said.

"You can tell him to do things a bit more, while Stephen is the old warhorse. When Stephen breaks the line, he pretty much passes it straight away, whereas Berrick runs another five or 10 metres."

Stirling Mortlock looks upon Barnes as more of a traditional five-eighth, whereas Larkham is more of a free spirit - not surprising considering that his background was in other positions before the No.10 was dramatically thrust on him mid career.

But Mortlock stresses that he feels as comfortable, just as he has been running off Larkham, knowing Barnes is the playmaker.

From a distance, it appears that Barnes is a more direct line runner, will take full advantage of a midfield break and is prepared to distribute far quicker to his supports. He has no qualms if the No.12 - particularly if it is Matt Giteau - shares the playmaker role with him.

Barnes and Giteau often play as a first and second five-eighth. Barnes appears to prefer the short, sharp pass to inside-centre, rather than the long cut-out ball. There is also no doubt Barnes has the more complete midfield kicking game.

Larkham is the drifter. He floats around the field, with the appearance of someone not exactly sure what he is going to do when he makes the break.

It is all part of the bluff - conning the opposition into believing he is doing something which he isn't. Larkham is the most calculating and unpredictable of all playmakers. He may look like he is cruising, but the mind is always ticking over - especially when he can quickly change the focus of the attack with long cut-outs, usually directed at the charging Mortlock.

"Stephen is a very rare individual," Mortlock said. "He knows how to read the opposition, both in analysis and in battle.

"On game day, he does things based on pure instinct, which other five-eighths probably wouldn't do.

"I haven't had much game time with Berrick, but from what I've seen he does his analysis very well, while his ability to implement the game plan is up there with quality players I've been involved with.

"His calling is good. Obviously Matt Giteau and George Gregan help him out in that area, but he is very diligent in his preparation."

The Wallabies captain told the Herald that the most marked difference between the pair was that Barnes was from the more tried and true five-eighth mould. Larkham had evolved from a far more individual make-up.

"What Berrick brings to the team is slightly different to what Stephen brings," Mortlock said.

"But we are very lucky that in the past few years our game has changed significantly to having less fulcrum on our No.10. Berrick has slipped into the team really well, and we guess we now vary it up a lot more - whether we fulcrum off Berrick or fulcrum off Matt Giteau. There's a little bit of a different spin on how we do things. Berrick is playing within our specifics and targets for the game, as opposed to someone going on what he reads at the time.

"Obviously being so young at this level, he is probably not as instinctive at the moment."

Mortlock obviously relishes playing alongside Larkham, because he provides such great service. But that's not to say Barnes won't, when required, play a similar role.

"Berrick still has a good long pass, but I don't think anyone in the world has a better longer passing game than Steve," Mortlock said. "But if I want the ball directly from Berrick, I'm sure he'll be very happy to give me it."

When asked if Larkham and Barnes aligned themselves differently during matches, Mortlock explained that this had more to do with what was going on around them.

"Again, going back to how our game has moved somewhat, we want our No.10 to be aligned, based on where the centres want him to be aligned," Mortlock said.

"So if we are getting quality go-forward ball, and the defensive line in particular aren't set, you want him to be as flat as he can be.

"Other times, when the defensive line has been set and they're coming at you, you can't have your No.10 too flat. With our mind-set recently changing, that helps Berrick out there.

"The onus is on the guys outside him directing him, more than him deciding where he should be."

Not surprisingly one of Barnes's favourite songs is With a Little Help from My Friends.