New Zealand have had a couple of crucial periods this summer.
Against Zimbabwe in Bulawayo at the start of November, their hosts were looking good for what would have been a famous victory at 287 for four, chasing 366 before Doug Bracewell's five-wicket haul in the afternoon won a 34-run victory.
At Hobart in December, New Zealand took all 10 Australian second innings wickets well inside two sessions to achieve a remarkable seven-run win. So they have become used to key sessions, and today's opening two hours will join that list.
This New Zealand team were written off as test chances after being relentlessly squeezed into submission by the South African pressure machine in their three ODIs. Five limited-overs games, including the T20 series, were lost on the bounce. What hope would they have in the premier form of the game?
Things might still go haywire in the coming days, but at least they have given themselves an opportunity. The issue will be whether they are good enough to capitalise on it.
Before tea, the ball wouldn't swing and captain Graeme Smith and Hashim Amla, who has feasted on the New Zealand bowlers in the ODIs, were working assiduously to press on to a strong position.
Up stepped Martin, who at 37 remains the country's premier seamer.
Forget all the talk about the promise of the younger brigade coming through. Martin leads this group and when Smith played sloppily away from his body in the first over after tea, he moved one wicket ahead of Chris Cairns into third overall for New Zealand behind Richard Hadlee and Dan Vettori.
Jacques Kallis and AB de Villiers, respectively Nos 2 and 4 in world test batting rankings, were swept aside with consecutive deliveries - the first to a fine catch at first slip by captain Ross Taylor, the second lbw to a ball which cut back.
Martin missed his hat-trick but his post-tea spell of 6-1-16-3 meant the game was on for New Zealand.
Amla, a cultured 22nd half-century behind him, was caught at slip cutting at Vettori and when Mark Boucher and Dale Steyn were whisked away, South Africa were on a slippery slope.
New Zealand would have been in even ruder health had Bracewell's no ball problems not returned to bite him, and his team.
Bracewell had Jacques Rudolph lbw, but had overstepped the line.
This was the third time this summer New Zealand have lost a wicket because of Bracewell's poor footwork. It's becoming something of a broken record, and needs to be sorted out pronto.
At least New Zealand didn't lose one of their two referral chances, umpire Billy Doctrove's poor eyesight on the initial no ball call negating the lost referral.
Veteran lefthander Rudolph averages 35 in tests, but 88 against New Zealand, and he carried on in that vein, cutting and pulling vigorously. By stumps he stood between New Zealand and slicing right through the South African innings.
Martin is up to 221 test wickets, and was New Zealand's most threatening bowler.
Bracewell, his bungle aside, toiled hard and well; Vettori was clever but left armer Boult disappointingly expensive, conceding 10 fours in seven overs.
