Samarth, who resumed the day at 118, led the batting charge with a 462-ball 235 as Karnataka scored runs at a brisk pace against a listless Jharkhand bowling attack to declare their innings at a mammoth 577 for 6 at Greater Noida Sports Complex Ground.
Samarth hit 24 boundaries and two sixes in his marathon innings which lasted more than 11 hours.
All-rounder Stuart Binny (97) missed out on a century by three runs while Kaunain Abbas hit 55.
In reply, Jharkhand were nine for no loss from five overs. They trail by 568 runs with all the first innings wickets in hand.
Jharkhand now face a herculean task of saving the match and their chance of winning it is virtually over. They can hope for a draw and wriggle out of the match with one point by batting sensibly in the remaining two matches.
Karnataka: 577/6 declared (Ravi Kumar Samarth 235, Stuart Binny 97; Ashish Kumar 3/78).
Jharkhand: 9 for 0 in 5 overs.
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