Youngest participant FM Aravindh Chithambaram, 13, stunned veteran GM Dibyendu Barua in 27 moves after the latter blundered to allow a sharp attack in a French Winawer.
The meet, earlier known as National A, is being held here after a gap of 36 years and is incidentally organised by Dibyendu Barua Chess Academy and All Sport Management.
India's second GM after Viswanathan Anand, Barua returned to action after a four-year hiatus.
In another upset, National Women's champion WGM Mary Ann Gomes won on time against second seed, S P Sethuraman in a complicated position which arose from the Sicilian Najdorf.
Top seed GM B Adhiban was held to a draw by IM Swayams Mishra, who held the upper hand for most part of the game.
Swayams was forced to draw by repetition when Abhiban neutralised his opponent's advantage.
GMs Lalith Babu, Deepan Chakravarthy, Abhijit Kunte, S Arun Prasad and Praveen Thipsay, too, were held to a draw by their lesser ranked opponents.
Altogether 15 GMs and 11 IMs are vying for the top honours in this 13-round Swiss league with the final round to be held on October 14.
All India Chess Federation will select top players for the composition of Indian men's team for various international meets in 2013 from this championship.
The winner will also get a berth in the World Cup next year to be held in Tromse, Norway.
With 2013 not being the Chess Olympiad year, star GMs like Surya Sekhar Ganguly, K Sasikiran, P Harikrishna, Parimarjan Negi and defending champion Abhijit Gupta have given the meet a miss.
Sports Minister Madan Mitra promised a sum of Rs 5 lakh for the meet. MORE
