Cricket: Kane Williamson wicket key for South Africa - Du Plessis

Kane Williamson will need to keep his eye on the ball for the rest of the series. Photo / photosport.nz

The spotlight will zero in on New Zealand skipper Kane Williamson this week perhaps more than at any time during his fledgling test captaincy reign.

Williamson has lost his senior wingman Ross Taylor, to a calf injury. Leave aside the loss of key bowler Trent Boult for now.

South Africa are quite clear how they rate New Zealand's batting group - Williamson, Taylor and four other blokes.

Now one of the two planks is gone, the tourists' sense a big opening.

At Dunedin in the first test, Williamson struck his 16th test century, equalling Taylor's mark and the pair now lie jointly one behind the New Zealand recordholder Martin Crowe.

Williamson's 130 was an outstanding innings and South Africa's captain Faf du Plessis made his admiration clear, albeit in slightly roundabout language.

"I said before the series that if we can get rid of Williamson and Taylor there's a lot of pressure on the rest of the batting lineup," du Plessis said.

"We couldn't get rid of Kane in the first test and they were successful as a unit. There lies the secret."

Williamson would probably bristle in defence of his other batsmen.

After all, Tom Latham is averaging 39.81 from 30 tests with six centuries. But he's in a rut - 10 at Dunedin followed 13 runs in his previous six ODI innings.

Jeet Raval is averaging 36.12 in his five tests, with three fifties; Jimmy Neesham has two test centuries and is going at 36.31, although four of his last five innings produced 13 runs.

Henry Nicholls averages 30.12 in his 11 tests and had success at Centurion against South Africa last year. Throw in wicketkeeper BJ Watling, whose doughty batting mainly at No 7 has produced an average of 38.45 from 50 tests.

By comparison, South Africa have considerable batting muscle, in the form of the world class but out of sorts Hashim Amla, du Plessis, opener Dean Elgar - man of the match in Dunedin with a 140/89 double to bump his average to 41.82 - plus mercurial wicketkeeper Quinton de Kock (average, 47.37).

But du Plessis' point has some validity: so much of New Zealand's batting muscle revolves around Williamson and Taylor.

Now consider Williamson averages 79.90 in eight tests at the Basin, against his overall average of 50.89 from 59 tests.

The second of his 16 tons was a fantastic defensive performance for 102 not out against South Africa's powerful seam trio of Dale Steyn, Morne Morkel and Vernon Philander in 2012 at...the Basin.

That was the first of his three centuries at Wellington, with the others being 242 not out against Sri Lanka in early 2015 and 104 not out to push New Zealand to victory against Bangladesh last January.

Williamson will lead New Zealand in a test for the 12th time today. His batting average from his previous 11 matches in charge is 60, 10 runs up on his overall mark. Captaincy seems to suit his batting.

Slice it anyway you like, but it's hard to underestimate the significance of the skipper over the next five days.