South Africa captain Faf du Plessis breathed a sigh of relief as rain bucketed down in Hamilton on Wednesday, washing out the final day of the third Test against New Zealand and ensuring his side sealed a 1-0 series victory.

The Proteas had been facing a massive battle to save the Test, entering the final day having been reduced to 80 for five and still 95 runs short of making New Zealand bat again.

Du Plessis, who would have been joined by Quinton de Kock at the crease had rain not intervened, said he had been prepared to defend all day.

"I was ready to come out and play my blockathon," du Plessis said. "New Zealand outplayed us in this game and deserved to win and they will count themselves unlucky.

"I'm pleased with another series win away from home but to be honest I think we played very much under par, especially the batting unit."

Du Plessis' analysis of his top order's batting issues on the tour was not restricted to their third Test first innings slump to 64-3 and then a collapse to 59-5 on Tuesday.

In the first Test, they were 22-3 after winning the toss before Dean Elgar rescued them with 140 and century partnerships with du Plessis and Temba Bavuma.

In Wellington, they were in trouble at 94-6 in their first innings before Bavuma and de Kock combined for 160 runs.

Elgar's century was the only one scored by the Proteas during the series and the batsmen who occupied slots five to eight in their lineup -- du Plessis, Bavuma, de Kock and Vernon Philander -- had four of their six top batting averages.

Elgar was the only top-order batsmen in the leading six, with fast bowler Morne Morkel holding the third best average of 49 courtesy of 40 runs in Wellington and two other not outs.

Du Plessis added that his side needed to ensure that those collapses did not happen again on their tour of England starting in May, before home series against India and Australia.

"In a Test match when the series is on the line you are looking for your players to front up and make it as hard as possible for the opposition to get your wicket," he said. "I thought... that didn't happen.

"But the good, strong teams find ways to win Test matches and series. And while we didn't play very well, we somehow found ourselves winning another away series."