Brendon McCullum at the top, Kane Williamson at first drop, Ross Taylor the ballast at No. 4 - it has been a rare occurrence in recent times that one of those has not fired for New Zealand. And when they have had a collective off day, someone has usually been on hand to bail them out.

The most extraordinary example was Luke Ronchi's record-breaking, unbeaten 170 off 99 balls against Sri Lanka in Dunedin - the highest score by a No. 7 in ODIs - when he added 267 for the sixth wicket with Grant Elliott.

This has been a breakthrough season for Ronchi at the international level and he is shaping as the X-factor in the New Zealand side, having shown he can both rebuild if an innings is in trouble or plunder bowling in the closing overs if a base has been set - and on occasions, such as Dunedin, do both in one stay at the crease.

"It all depends on the game situation," Ronchi said of his mindset in the middle. "My role is to finish off an innings as well as I can, but if we have lost early wickets then I just go out to bat."

Since Ronchi crossed the Tasman in 2011 and returned his allegiance to the country of his birth, New Zealand have been desperate for him to become a success in the one-day team. Domestically he carried all before him and had shown glimpses during his brief Australia career of the destructive capabilities he possesses with a 22-ball half-century against West Indies in St Kitts in 2008.

That was his last one-day appearance in the green and gold, but his return to international level five years later did not begin easily. Miscast as an opener, although with understandable thinking from New Zealand who had been seduced by his power, he limped through his comeback series against England in 2013 and the subsequent Champions Trophy to end with 47 runs in six innings prompting questions about technique and temperament.

The selectors kept faith with the man but acknowledged he was in the wrong position. On the tours of Bangladesh and Sri Lanka later in 2013 he was down in the middle order and glimpses emerged of the impact he could have when he made 49 off 26 balls during a reduced chase in Hambantota.

Although the big score was still eluding him, that was often more due to circumstance in that New Zealand's top order was becoming more productive and Ronchi's opportunities were often very late in the innings. What he needed, in a perverse way, was for New Zealand to find themselves in a hole - and even better if it came against a strong attack. How about Dale Steyn, Morne Morkel and Vernon Philander and some spicy pitches?

That exact situation presented itself during the early season ODI series against South Africa last October, a time of year when international cricket had never before been played in New Zealand, leaving a fearsome visiting pace attack licking their lips. Twice in the space of three days in Mount Maunganui, Ronchi walked to the crease with his team in a mess: 68 for 5 and 69 for 5.

He produced innings of 99 and 79 and, though neither turned the result around, they were solid evidence that Ronchi had a two-fold game. Crucially he was still playing by his natural instincts but his defensive technique had been tightened. When his New Zealand career stuttered at the start it would have been easy to question himself, doubt the game that had carried him twice to international level.

Now, leading into a World Cup and with the comfort of a maiden century under his belt, Ronchi is very much at ease with his gameplan. "Unless it's crazy green that's the way I've always batted. For me, to have a positive frame of mind works best. If I go the opposite way then I'm not playing to my natural ability."

Although McCullum's decision to hang up the keeping gloves for good to save his troublesome back perhaps bought Ronchi a little extra time, it is not inconceivable that he was one poor series away from his second coming as an international cricketer being aborted. "To be where I am now is not something I thought would be the case a few years ago," he admitted. "I am really grateful for the position I'm in."

His New Zealand team-mates, and no doubt the supporters, are also grateful to see him in his position in the middle order.

Andrew McGlashan is a senior assistant editor at ESPNcricinfo