Karnataka made a cautious start making just 32 runs in the 15 overs they faced on the second day of the match at the slow Jamia Millia track here.
At stumps, Robin Uthappa was batting on 14 with Barrington Rowland on 17.
The day, however, belonged to Jadeja, who not only scored his second century of the season, but made useful partnerships with Rajat Bhatia (50) and Vijay Dahiya (49) after the team lost centurion Shikhar Dhawan very early in the day.
Jadeja scored 103 runs in 202 balls with the help of 15 fours and declared immediately after completing his ton to give his bowlers atleast an hour to make early inroads into the visitors batting lineup.
Earlier, Delhi, resuming at 205 for 4, recieved an early jolt when Dhawan fell to left-arm spinner Sunil Joshi after adding just nine runs to his overnight score.
Dhawan's departure did not affect the skipper much as he walked in with confidence and in the company of Bhatia added 70 runs in 25.1 overs for the sixth wicket.
Jadeja then stepped up the tempo to collect 126 runs from 38.2 overs with Dahiya.
Dahiya was unlucky not to complete his half century as he was run out just a run short of the mark.