Tom Latham needs to "go back to basics" to try and escape his lean run of form, according to New Zealand batting coach Craig McMillan, after making a "poor decision" in the second innings in Wellington.

Latham is set to retain his place in the squad for the final Test against South Africa in a season which has nose-dived for him since the one-day series against Australia - which coincided with him being given the wicketkeeping gloves. He has made scores of 10, 8 and 6 in the two Tests which follow his one-day run of 4, 7, 0, 0, 2 and 0 after a productive earlier part of the summer which included career-bests in both ODIs (137 v Bangladesh) and Tests (177 v Bangladesh).

His overall Test record remains solid, with an average of 38.64, and his average opening the innings is the fifth highest among New Zealand batsman to have done it in 20 Tests.

He was dismissed twice by Morne Morkel in Wellington. In the first innings, he edged a good delivery, angled across him, to slip but in the second tried to drive ball and gave a catch to gully.

"Tom's obviously going through a tough patch but we know what a quality player he is, and has been for a number of years," McMillan said. "He's got six test hundreds and bats in perhaps the toughest position in the order, and has done well for a long period for us.

"It's about him getting back to basics. One of his decisions was poor, to drive when it wasn't full enough to drive, and he acknowledged that. We need to get him back to making those good decisions and everything else will flow from there."

The knock-on effect of having an opener bereft of confidence against a high-quality attack is regularly exposing the No. 3 early in an innings. However, McMillan believes New Zealand have "the best in the world" in captain Kane Williamson.

"I think he's the best No. 3 in the world," McMillan said. "The reality is that when you bat at No. 3 you can be an opener, new-ball bowlers are fresh in difficult conditions. Kane is very mentally strong around that, it's a position he enjoys so I don't see any point at all in tweaking that."

The longest he has been able to wait to bat this season is 16.1 overs when Latham and Jeet Raval added 54 against Bangladesh in Wellington. While Raval has enhanced his reputation against South Africa with two half-centuries, the hope that a return to red-ball cricket would revive Latham after his one-day struggles has yet to come to fruition.

Kane Williamson demonstrates a shot to batting coach Craig McMillan Getty Images

In Dunedin, Williamson strode out in the sixth over. In Wellington, the seventh and fifth. In the first Test, he scored one of the finest hundreds of his career - which lifted him to No. 2 in the Test rankings - but at the Basin Reserve completed his lowest return when he has batted twice in a Test. It was one game, for one of New Zealand's finest batsmen, but could not have come at a more inopportune moment with Ross Taylor missing.

Taylor may return for Hamilton, although it sounded unlikely on Sunday with McMillan saying he would not be rushed if not fully fit, but there is no thought being given to trying to allow Williamson some breathing space in the batting order.

Williamson's record at No. 3 certainly stands up to scrutiny. He has played 90 of his 109 innings at No. 3 since 2011, and has scored 4346 runs at 53.65: he is the ninth-most prolific No. 3 of all time.

Despite New Zealand's rapid slide to defeat, there were some encouraging signs that the batting burden does not always have to sit on Williamson and Taylor. Henry Nicholls scored a maiden Test century and then Raval made a gutsy 80 when he fought through a period of rapid short-pitched bowling from Morne Morkel and Kagiso Rabada.

"I thought it was a really good hundred. He's been building to that for a while," McMillan said. "We've known he's had that short of performance in him. He's works really hard, has a lot of strong traits, and I thought that was the best we've seen him bat in terms of decision making, showing good intent. That's really encouraging. There were a couple of positives, I know a lot of the talk is around the negatives and that's understandable after a day like yesterday, but I thought Jeet Raval played really well too."