The 19-year-old Indian played a fashionable line with the white pieces against GM Abdelrahman's Sicilian Najdorf play, at the Mount Litera International School at Bandra Kurla Complex here.
A couple of minor inaccuracies by the Egyptian allowed Nair to unleash a powerful attack that ended in a spectacular victory in his maiden tussle against a Grandmaster.
Another Indian who tasted success over a GM was Bihar's Saurabh Anand who defeated his sixth-seeded Armenian opponent GM Karen Movszszian.
Among other minor upsets, Indian hope GM Diptayan Ghosh could only draw with Pune's Nikhil Dixit who is rated almost 600 points below the former.
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The juniors event, held concurrently, saw contests move along the expected lines.
A group of six youngsters led the tournament at the end of four rounds with 4 points each.
Results: Open category (top 10 boards with ratings in brackets): GM Diptayan Ghosh (2570, IND) 2 drew with Nikhil Dixit (1919, IND) 2; GM Adam Tukhaev (2516, UKR) 2 bt CM Karthik Kumar Pradeep (1899, IND) 2; WFM Divya Deshmukh (1920, IND) 2 lost to GM Valeriy Neverov (2478, UKR) 2; IM Shyaamnikhil P (2451,IND) 2 bt Harshavardhan G B (1870, IND) 2; Sanjeet Manohar (1914,IND) 2 lost to Himal Gusain (2448, IND) 2; IM Saptarshi Roy (2418, IND) 2 bt Vigneshwaran S (1867, IND) 2; Sanjeev Nair (1899, IND) 2 bt GM Hesham Abdelrahman (2408, EGY) 2; IM Sayantan Das (2371, IND) 2 bt Sradhanjali Jena (1864, IND); WGM Toma Katarzyna (2322, POL) 2 bt Aakash Sharadchandra Dalvi (1818, IND) 2; Jeet Jain (1866, IND) lost to CM Aditya Mittal (2068,IND) 2.