After further strong Ranji performances in the 1999/2000 season, taking 17 wickets at 10.11 including a haul of 12/93 against Vidharbha, Kartik made his debut in February 2000, playing in both Tests against South Africa at Mumbai and Bangalore as India sought a second spinner to accompany Anil Kumble, after Harbhajan Singh's performance in the role in the previous season had been deemed inadequate. Kartik performed steadily, taking six wickets at 33.5.

Kartik was selected in 2000 for the first intake of the National Cricket Academy in Bangalore, after earlier having made his Test debut in early 2000 in a home series against South Africa. However, his stay was cut short along with that of Harbhajan Singh, when they were expelled by the director Hanumant Singh over disciplinary issues.