Greg Growden, after overcoming a serious bout of hay fever from putting on the musty old musty Wizard suit, tipped all four quarterfinal winners last weekend. He has bravely decided to push his luck by predicting what will happen in the semi-finals.

New Zealand v South Africa

The crucial factors: This is the biggest and most compelling rivalry in world rugby, and so both coaches will have no trouble getting players in the required mental state for this semi-final. It will be more a case of having to calm some of their more excitable squad members. That's where the All Blacks have the advantage. They remain such a composed group, the ultimate example of a side who know how to look after themselves and not lose perspective, understand the importance of team standards, and what to do when it gets tense. They are the best counter-attacking team going around, thriving on opponents who blunder under relentless pressure. They are also the masters of applying the pressure that leads to those blunders.

The All Blacks weren't too concerned about their lowbrow performances during the pool stage, knowing it was more important to hit their peak in the final weeks - prompting the best effort of the tournament so far when overwhelming France last weekend.

The All Blacks celebrate another try against France© Stu Forster/Getty Images

The Springboks, meanwhile, have instead been thriving on high emotion and adrenaline. Their ridiculous first-round loss to Japan, for good reason, shook them up enormously - in particular their coach Heyneke Meyer, who doesn't seem to have yet got over it; and so to ease their high stress levels it's not surprising to see they have reverted to their traditional ways to get out of trouble. With it has come tedious one-out bash-and-barge football. It has got them to the semi-final but much more will be required if they want to be one of the finalists.

New Zealand are good at protecting the middle of the field, so South Africa need to be more broad minded and use their finishers - Bryan Habana, JP Pietersen and Willie Le Roux - far more. Against Wales last weekend, Habana and Pietersen were wasted.

Man of the match: Jerome Kaino (New Zealand). This is a game bound to be won up front, and the All Blacks have an important asset in their blindside flanker, who is so industrious at the breakdown. The Springboks forwards will try to over-power their All Blacks counterparts, and Kaino's excellent defence and ball-raking skills could prompt turnovers. As importantly, he is one of the fastest No.6s going around, so expect him to be nearby if there is an All Blacks counter-attack.

The influence of the referee: Apart from the Craig Joubert quarterfinal blunder, the standard of refereeing during this tournament has been pretty good. Among the most consistent has been Frenchman Jerome Garces, who appears relatively eager to give teams some freedom. How he handles the breakdown will be crucial as both teams will be trying to get away with as much as possible. He can be fastidious - especially if he is not happy with how either team is scrummaging. Garces is a bit of an unknown factor.

South Africa got out of jail against Wales© Dan Mullan/Getty Images

Potential of an upset: A possibility. South Africa always lift when they play New Zealand, and these encounters continually inspire extraordinary football. A lot will depend on whether the Boks adopt a bold approach to be more expansive. If they persist in being dinosaurs and having one forward after another taking the ball up, or being one out when attacking wider, the Springboks are no hope as they will just walk into the All Blacks' midfield booby trap.

Tip: New Zealand by 7.

Australia need more structure in attack this weekend© GLYN KIRK/AFP/Getty Images

Australia v Argentina

The crucial factors: The level of Australia's performance hinges so much on how well their scrum is operating and if their playmaker, Bernard Foley, is on top of his game. Against England and Wales, the Wallabies pack was exceptional and Foley's efforts astounded all. The Scotland quarterfinal was somewhat different. The Australian scrum was suddenly under threat, loose head-prop Scott Sio was repeatedly penalized, and Foley looked hesitant. The Australian game dropped right off, and they would have been heading back to Sydney some days ago but for a contentious refereeing decision in the final minutes. Yes, Australia are lucky to still be here, but they know they have to take full advantage of a rare second chance. Again it revolves around the scrum and Foley, and Argentina know that. The Pumas have the pack to worry Australia, and the pace in their game to put Foley under pressure. So it will be tight.

David Pocock remains an Australian injury concern© Dan Mullan/Getty Images

Argentina are hoped by the uncertainty surrounding two of Australia's key performers will play. If David Pocock is forced out for a second week with his calf complaint, it is an enormous boost for the Pumas. Without Pocock last week, Australia's work at the breakdown nosedived. Israel Folau, another in doubt, will not be as big a loss, as Kurtley Beale, as shown against Scotland, can adequately cover him at full-back.

Man of the match: Michael Hooper (Australia). With the threat of Pocock again not being there, Hooper really has to step up this week in both his breakdown work and leadership. Hooper revels in the big forward encounters, and so he should relish an Argentinean stouch. He often performs well against the Pumas.

The influence of the referee: Australia will have no qualms with Wayne Barnes. Their record under him is startling. As the Sydney Daily Telegraph's Iain Payten reminded us this week in one of his articles, Barnes has officiated 12 Wallabies Tests resulting in 12 Australian victories. He has only refereed one Australia-Argentina Test - in Rosario two years ago - and that resulted in a record 54-17 victory. Neither team can complain about not knowing what Barnes is up to. During a match, he is a constant chatterbox, endlessly telling the players what he wants, what he is unhappy and happy with. Some players must sometimes wish they were wearing earmuffs.

Juan Imhoff and Argentina are the tournament's entertainers© Phil Walter/Getty Images

Potential of an upset: Very, very high. Australia are firm favourites but they are suddenly looking vulnerable while Argentina have been the big improvers of this World Cup, enthusing all with their expansive game plan. The Pumas can very easily win this. No longer are they just the masters of the power game. After committing opposing forwards with several midfield charges, the Pumas' game plan now involves width, decoy runners and a backline opting for speed and breaks rather than trying to repeatedly boot the ball in front of their marauding forwards. They have constantly tested defences but will find Australia of a higher calibre. They will not have as much freedom against the Wallabies as they did against Ireland, as Australia boast an excellent defensive pattern out wide.

Tip: Australia by 2.