Tahir holds the No 1 bowling spot in both T20 and ODI cricket, and recently topped the ODI charts following his performance in the 5-0 series win against Sri Lanka - where he finished as the second-highest wicket-taker with 10 wickets.
He has developed into an x-factor player for the Proteas in the short format of the game, with captains, AB de Villiers and Faf du Plessis, acknowledging the value he adds in the respective formats.
The 37-year-old, who has played 69 ODI's and 30 T20I's in his six-year career, continues to get better with age and hard work.
"I have been working very hard," he said in Auckland on Thursday.
"It's not easy to perform in every series but as long as I am performing for the team and the captain and coach are happy then I am happy.
"It is special for me," he said of the rankings.
"When I started playing cricket I never thought that I would be the No 1 bowler one day. It's due to all of the hard work I have put in, I'm excited, there are a lot of good players around the world.
"Being No 1 is a great achievement, I'm grateful to the team I am playing for, it's an honour to play for South Africa and the boys have helped me over the years and made me the bowler I am today. Hopefully I can continue to put in the performances to stay at the top."
The Proteas were forced to practice indoors on Thursday due to the inclement weather ahead of the match at Eden Park on Friday, but remain aware on focusing on the elements within their control despite the disruptions to their preparation.
"We had a full session yesterday (Wednesday)," Tahir said.
"We have just played a series so the guys are in good touch. I don't think it will bother us too much if we don't have any other sessions, we have been playing good cricket, everything in the camp is going well."
The lone T20I at Eden Park in Auckland on Friday (08:00 SA time).
South African limited overs squad:
Faf du Plessis (captain), AB de Villiers, Hashim Amla, Farhaan Behardien, Quinton de Kock (wicketkeeper), JP Duminy, Imran Tahir, David Miller, Chris Morris, Wayne Parnell, Dane Paterson, Andile Phehlukwayo, Dwaine Pretorius, Kagiso Rabada, Tabraiz Shamsi.
New Zealand Twenty20 squad:
Kane Williamson (captain), Corey Anderson, Trent Boult, Tom Bruce, Lockie Ferguson, Colin de Grandhomme, Glenn Phillips, Colin Munro, James Neesham, Luke Ronchi, Mitchell Santner, Ish Sodhi, Tim Southee, Ben Wheeler.