India, who lost their top ranking to England after their 0-4 whitewash in 2011, got back to the pinnacle by virtue of their crushing 3-0 series win against the Proteas at home, last December.
India now have 110 ranking points and have one point more than Australia, who are second in the list with 109 points in their kitty. South Africa are now third in the rankings.
The joy of reaching top spot for India can be shortlived if Australia win their home Test series against New Zealand by 1-0 margin as the Aussies will then displace Kohli and Co. from the numero uno position.
South Africa have not won a Test match for more than a year with their last victory coming against the lowly West Indies. Even if they beat England in the fourth Test at the Centurion, they would not improve from their third position.