Rugby World Cup 2011: Guscott on Ireland v Australia & Wales v Samoa

Key men (clockwise from top left): Wales centre Roberts, Australia fly-half Cooper, Ireland flanker O'Brien and Samoa number eight Stowers

Two of the definitive matches of the 2011 World Cup pool stages take place this weekend as Ireland look to upset Australia on Saturday and, on Sunday, Wales try to avoid a repeat of their 1991 and 1999 humblings by Samoa.

Beat Australia and the draw opens up invitingly for Ireland; lose to Samoa and Wales will be staring at a repeat of their disastrous exit in the group stages at the 2007 World Cup.

Ex-England and Bath centre Jeremy Guscott tells us what we can expect to see in the pick of the weekend's World Cup games in New Zealand.

TACTICS - WHAT GAMEPLANS CAN WE EXPECT TO SEE?

Australia are incredibly talented and a serious threat but their gameplan is straightforward.

Unlike South Africa, who often look to kick, chase and defend, the Wallabies aim to go through phases and build up some momentum.

That means they like to get the ball into the hands of half-backs Will Genia and Quade Cooper very quickly.

They have always had good backs but now seem to have found the solution to their front-row problems and they have become pretty dynamic in the scrum.

Add to that the potency of captain James Horwill in the second row and a fierce back row of Rocky Elsom, David Pocock - if fit - and Radike Samo and they have a formidable pack.

That means they may now want to soften teams up a bit more than they used to before unleashing their backs.

Sexton is handed another chance to cement his status as first-choice 10

Ireland won't be setting out purely to subdue Australia, they'll be aiming to play their own game and I think it's right coach Declan Kidney has stuck with Jonathan Sexton at fly-half, despite his poor kicking in their opening win over the United States.

They will compete fiercely at the breakdown because, although Pocock will probably be there quicker than Ireland's Sean O'Brien, I think the Irish second row and back row are slightly more mobile than Australia's.

Wales will hear echoes from history on Sunday when they face Samoa, who beat them in the 1991 and 1999 World Cups.

Samoa are pretty hardcore and no-one should ever be surprised by them these days. They are quick, powerful athletes and even their scrum-half was bashing people out of the way in their opening win against Namibia.

The only areas of concern for them are discipline and the technicalities - the line-out and scrum - although they are improving.

Wales play a skilful passing game but one important difference these days is their increased physicality, best typified by Jamie Roberts in their opening defeat by South Africa.

Their back row also shone against the Boks and they will hope to gain an edge in the line-out and scrum to give them the platform to launch their talented runners in the backs.

KEY PLAYERS - WHO ARE THE MAIN MEN IN AUCKLAND AND HAMILTON?

I like maverick Australia fly-half Cooper. Once it gets into his hands, the Wallabies can become very unpredictable. He plays what he sees in front of him and follows his instinct.

Open-side flanker Pocock is arguably now the best number seven in the world and Ireland will be aware they can't afford to give him freedom to control the breakdown.

That means plenty of work for flankers O'Brien and Stephen Ferris. They will also have to close down the space available to Cooper.

Hopefully the decision to back Sexton will give him belief and he can now play like we've seen him play for Leinster, particularly that memorable performance in the Heineken Cup final win over Northampton, when he showed he was one of the best 10s in the northern hemisphere.

Roberts' collision with Samoa will not be for the faint-hearted

In the other game Alesana Tuilagi, one of my players to watch before the tournament kicked off, grabbed a hat-trick for Samoa in their opening match against Namibia and the thunderous Leicester wing will always be a threat.

George Stowers, the former London Irish number eight who has signed for Welsh region the Ospreys, was man of the match against Namibia - he is powerful in defence, powerful with the ball in hand and links play very well.

Against South Africa, Wales centre Roberts played the best game I've seen from him for a long time and he will need to produce that form again.

He was very direct, carried punishingly and took two or three players with him. Let's not forget how physical the South Africans can be.

Sam Warburton was supreme on the open-side and forwards Dan Lydiate, Toby Faletau and Alun Wyn Jones all shone - I hope they've recovered enough to be able to put together a similar performance on Sunday.

The only thing I would have changed is to put James Hook at 10 - not because Rhys Priestland didn't play well but because Hook is better and more skilful in my opinion.

MINDSET - WHAT SHAPE IS EACH TEAM IN MENTALLY?

I don't think the four warm-up defeats and laboured win over the USA will have affected Ireland's confidence because, at some stage, you have to just think, "We can't keep playing that badly".

They are a team full of northern hemisphere superstars, stuffed full of Lions from 2009, and they should be the best team north of the equator. But they are performing so poorly it beggars belief.

Australia will be full of confidence. They won the Tri-Nations and pulled away from Italy well after half-time in their World Cup opener.

I'm interested to see how Wales play after their heart-breaking defeat by South Africa because their performance will either have really buoyed them up - and given them the belief they have something to build on - or it will have taken too much out of them.

In the past, I believe they've been mentally frail but they showed none of that against the Springboks. They played with plenty of skill and made very few errors.

Back in 1991 Samoa pulled off one of the great World Cup shocks when they beat Wales - and the Welsh also lost to Fiji in the last World Cup.

Only six of the 22-man squad from four years ago are in the 2011 squad but it could happen again if they don't play well.

Wales could quite easily go behind and that's when the mental demons come in.

PREDICTION - SO WHO'S GOING TO WIN THEN?

Ireland will have to be at their best or else they will find themselves on the end of a bit of a hiding but I expect a much better performance than in their first game. I don't think it will be by a big margin.

If Ireland play their best rugby, I wouldn't be surprised if they won.

Should Wales play as well as they did against South Africa, they will beat Samoa - but they need to bring the same physicality.

They need to understand they were the best team against the Boks and only lost because they didn't take their chances.

If they believe that and take it into the Samoa game they will win. I'm not saying they will win easily but they will win.

Jerry was talking to BBC Sport's James Standley.