YOKOHAMA – Defending champions New Zealand take on South Africa in their opening Pool B match of the 2019 Rugby World Cup on Saturday.AFP Sport looks at five key battles of the blockbuster showdown that will likely determine the pool winner:SAVEA VS KOLISIArdie Savea is currently touted as the world’s best back-row forward. The 25-year-old Kiwi and brother of winger Julian – the highest try scorer at the 2015 World Cup and now playing for Toulon in France – is dynamic in the loose, uncompromising in defence and avoids over-committing at ruck time.Standing 1.87m, Savea is one of the smaller All Black blindsides in recent years, but his destructive running meant he was too good to be left out and he is seen as the perfect foil for openside Sam Cane and number eight Kieran Read.But he will face a stern challenge from South Africa’s first-ever black captain Siya Kolisi.The talismanic Stormers flanker has been a key part of the Rassie Erasmus-led turnaround of the national team and stands out as a more than able ball-carrier in an abrasive Bok forward pack.BARRETT/MO’UNGA VS LE ROUX/POLLARDBeauden Barrett, a former two-time World Rugby Player of the Year, has been moved to full-back by head coach Steve Hansen to accommodate Richie Mo’unga in the number 10 shirt.It doesn’t seem to have hindered him, with Barrett’s talent and speed in open play, especially on the counter-attack, marking him out as one of the world’s most dangerous players with the ball in hand.The flexible Barrett has said he is equally happy to play at 10 or 15.On the Springbok side, full-back Willie Le Roux is also a devastating open-field runner and capable under the high ball, while Handre Pollard is an out-and-out fly-half, armed with a booming kick that will test Barrett to the max.READ VS VERMEULENAll Black number eight Kieran Read is a veteran of 122 Tests and has taken on the captaincy seamlessly since the retirement of back row partner in crime Richie McCaw. A lot of the work Read does is not flashy, but devastatingly effective.His Bok opponent is the also uncompromising Duane Vermeulen, a much-travelled forward who is a damaging runner in the loose and like most good Bok forwards, adept at the breakdown.Read appears to be relishing the match-up. “He’s a top bloke, very aggressive, a big man who loves to carry and tackle hard. I enjoy that challenge,” Read says of Vermeulen.SMITH VS DE KLERKThe battle of the chirpy scrum-halves pits Aaron Smith in black against Faf de Klerk in green and gold.Smith is a veteran of 87 Tests for the All Blacks, proving a crucial link between the pack and backs.De Klerk has thrived since joining English Premiership club Sale, honing his kicking game and decision-making. “The challenge for me is to put them under pressure… and from a tactical side, kick well and get some quick ball,” says De Klerk.WHITELOCK VS ETZEBETHBok lock Eben Etzebeth touched down in Japan under the shadow of an alleged assault and racial abuse of a homeless man in South Africa. The star enforcer, who has taken on the mantle left by greats Bakkies Botha and Victor Matfield, denies the charges – with the investigation still ongoing – and will be looking to put the focus back on his on-field performance.He will come up against Sam Whitelock, with All Black Brodie Retallick missing the game through injury. Whitelock, seeking to become a three-time winner alongside Sonny Bill Williams and Read, is a canny operator, a good go-to ball carrier who does a lot of the unseen clearing out work.“It’s one of those Test matches that every kid growing up wants to play,” says Whitelock.“Having that opportunity to play South Africa at a World Cup in the opening game is pretty cool.”