But after 21 wickets between them in the first 3 matches helping India to a 3-0 lead in the 6-match series, one can safely say that these two are vital cogs in the Indian line-up.
So what is it that has given the two so much purchase? How are the two wrist-spinners achieving so much success on pace-friendly tracks?
Before this series began, South Africa were on a 17-match unbeaten streak at home in ODIs. But that record has turned on its head with India's spin duo wreaking havoc by bowling slow.
They seem to be able to generate turn from any surface but it is the slowness which is really causing problems. The pace of their deliveries has been between 48mph and 54mph.
To put things in perspective, Imran Tahir's deliveries are paced between 53mph and 63mph. In other words, Tahir’s slowest delivery is still faster than the fastest balls bowled by Chahal or Yadav.
And without their two most experienced batsmen - AB de Villiers and Faf du Plessis - South Africa are really struggling.
Having picked up 5 of the 8 South African wickets that fell in the series opener in Durban, Chahal and Yadav were especially ruthless in the second match at the Centurion. Chahal finished with career-best figures of 5/35, helping to reduce the Proteas to 118, their lowest total on home soil.
In the post-match conference, skipper Virat Kohli heaped praise on his spin duo. "The pitch was harder than Durban and the spinners used it. We knew we won’t get grass on the pitch because when it’s seaming, it can be anyone’s game. We knew the wickets would be hard and dry and knew our wrist spinners can get it to turn anywhere. They just didn’t give South Africa any chance."
So hapless were South Africa that they employed five wrist spinners in the nets ahead of the third match at Cape Town. But it made no difference as Chahal and Yadav picked 4 wickets apiece, inflicting a 124-run defeat on the hosts. They are getting stronger with each performance and have sent out a warning to all the teams across the world.
With the batting already solid and the bowling slowly getting together, India are really playing like the world number one team at the moment. With the 2019 World Cup just over a year away, things look really promising at the moment for Team India.