Playing black side of Steinitz Defence of Ruy Lopez opening, Koustav sacrificed his rook for bishop and pawn on 39th move to garner full point against his fancied rival after 20 more moves.

Earlier in the fourth round Koustav shocked fifth seed Sethuraman while in the third round he held top seed B Adhiban.

In other important fifth round encounters, former champion GM Lalith Babu M R (PSPB) defeated GM r Aryan Chopra ( Delhi ) while much anticipated top board battle between young GMs D Gukesh (TN) and Arjun Erigaisi (Telangana ) ended in peace treaty after 46 moves arrived out of Semi Slav- Botvinnik System.

At the end of fifth round matches, second Arjun Erigaisi along with D Gukesh, Lalith Babu M R, Koustav Chatterjee and Commonwealth champion Abhijeet Gupta, who beat International Master Aditya Mittal are sharing the lead with four and half points.

A pack of 14 players including top seed A Adhiban are now trailing behind the leaders with a drift of half point.