Imran Tahir has said it is "very special" to be ranked the No. 1 bowler in both ODI and T20 cricket. He completed the double when he went top of the one-day table after South Africa's 5-0 victory over Sri Lanka where he claimed 10 wickets.

Tahir began that series with a Man-of-the-Match performance of 3 for 26 at Port Elizabeth and only in the high-scoring Cape Town match, where Sri Lanka replied with 327 to South Africa's 367, was he punished as he conceded 76 off his 10 overs. Even then he claimed two wickets to snuff out Sri Lanka's brave chase.

It's that skill of taking wickets, alongside his control, that makes him such a valuable asset to South Africa's white-ball sides. In recent times he has rarely failed to deliver a breakthrough for his captain - whether that is Faf du Plessis, AB de Villiers or Farhaan Behardien - and his last wicketless ODI was 10 games ago. He has been integral to South Africa's winning run which stands at 11 ODIs.

Tahir was twice previously ranked No. 1 in ODIs, when he briefly held the top spot during the 2015 World Cup before being leapfrogged at the end of the tournament by Mitchell Starc, then again in October 2015, and there is a chance of a bowl-off for the position in this series against New Zealand with Trent Boult, the No. 2-ranked bowler.

"When I started cricket I never thought I'd be No. 1 bowler, it's all the hard work I've done and I'm very excited," Tahir said. "There are a lot of good players in world cricket and coming top of that is a really good achievement and I'm really grateful.

"It's an absolute honour playing for South Africa, the boys have helped me over the years and made me the bowler I am today. Credit goes to them as well. I'll try and stay in the spot as long as I can but there are some other brilliant cricketers."

Tahir has not been able to produce the same success at Test level. His 20 appearances, the last of which came against India in Delhi, have brought 57 wickets at 40.24 and South Africa have moved on from him in that format.

However, with the white ball he has certainly grown older gracefully. "He doesn't bowl bad balls anymore," AB de Villiers said last month. "He always used to take wickets but now you don't see bad balls, which makes him really difficult to play."

When Tahir was asked what advice he would give Ish Sodhi, the New Zealand legspinner he could go up against over the next few weeks, he gave an insight into what had made him such a successful bowler.

"If I was him I'd work harder, I'm not saying he isn't but that's my advice because when I started like him I didn't know my game or use my variations," Tahir said. "I just bowled leggies, but then I worked hard to try to find how what would work for me in international cricket. Coming from South Africa is not easy because the pitches aren't spin-friendly, so I had to work out how to adjust."

They are skills that will serve him well in New Zealand, too, where - as Sodhi could no doubt attest to - conditions are not what legspinners dream of. Tahir has previously played three ODIs against the hosts in the country, the most recent of them the 2015 World Cup semi-final where he was wicketless but conceded just 40 in nine overs in the high-scoring contest, and New Zealand are aware of the impact he could have.

"He's a great operator for South Africa, and any team he plays for," Kane Williamson said. "We've played a lot against each other. It's important we play him well."

A few batting line-ups of late have found that easier said than done.

Andrew McGlashan is a deputy editor at ESPNcricinfo