The third wicket duo, who joined forces at the fall of openers Mayank Agarwal and R Samarth with only 4 on the board, compiled a 219-run stand to remain unbeaten at stumps in a team total of 223 for 2, still 102 runs adrift of Assam's first innings tally of 325 at the Bandra Kurla Complex ground here.
Uthappa, who struck two sixes and 12 fours in his 206-ball innings remained unconquered on 108, his first 20-plus score of the season and his 21st first-class hundred in his 126th game.
Dropped on 0 and 85, the 24-year-old batsman remained unconquered after facing 198 balls and with the help of 13 hits to the fence.
The duo put to sword the Assam attack which had its tails up after packing off Agarwal and Samarth for ducks in the second and third over respectively, Krishna Das and Arup Das being the respective wicket takers.
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Earlier, resuming at last evening's 268 for 6, Assam were dismissed for the addition of 57 runs. Stuart Binny gave an early break for Karnataka by sending back overnight unbeaten batsman Sarupam Purkayastha in the third over for 59 before leggie Shreyas Gopal mopped up the last three wickets.
Amit Verma was stranded on 166 off 316 balls and inclusive of three sixes and 23 fours as he ran out of partners. He was 125 last evening.
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