Kamal Chawla and local challenger Brijesh Damani also stormed into the quarter finals, while nine-time world champion Geet Sethi's poor run continued.
In two hours best of five frames match, Kothari made his intentions clear winning the first frame by 48 points against Mehta, who came here winning the Asian championship in Doha less than 10 days ago.
However, Mehta shot back in the next two frames with a comfortable margin. But Sourav applied brakes on Mehta's progress winning the fourth frame 73-34 to take the match into the decider.
The local lad showed amazing maturity as he potted with perfection to clinch the frame 65-19 with a stunning 3-2 win.
Chawla from Group C remained the first one to enter into quarter finals with an all-win record.
He defeated veteran and nine time world champion Geet Sethi 3-1 to make the knockouts.
More From This Section
In a must win match, India No 3 and local boy Shahbaaz Khan failed to deliver his best as he was blanked 0-3 to Indian junior champion Laxman Rawat of Delhi.
Another local challenger Brijesh Damani also confirmed his last eight berth with a 3-1 win over Devendra Joshi in close encounter.
Down 0-2, Joshi pulled back the third one and gave tough fight in the fourth frame too. But Damani stepped up the ante to go ahead of Joshi and sealed his quarters berth.
Former Asian snooker champion Alok Kumar and former World No 3 Manan Chandra also registered identical 3-0 wins over Manish Jain and Rohit Rajgaria respectively.
Alok, in the second frame, registered a break of 77 points.