International Master Neelotpal Das of India (3.5 points) shocked Grandmaster and compatriot Pendyala Harikrishna (2.5) on a day of upsets in the fourth round of the Commonwealth chess championship in Mumbai on Tuesday.
Another Indian Grandmaster, 15-year-old Koneru Humpy (1.5 pts) crashed to her second successive defeat, losing to Prathamesh Mokal (2.5) of India in a systematic play.
Humpy, who had lost to International Master Ravi Hegde in the third round on Monday, had herself to blame for the defeat, as her lack of preparation in Sicilian defence was astutely exploited by teenager Mokal, who scored the second win of his career over the former World junior girls' champion.
Top seeded Uzbekh GM Rustom Kasimzanov (3.5) was held to a draw by Vietnamese GM Guyan Anh Dung (3.5) in a keenly-contested battle in queen pawn opening. Second seeded Indian GM Krishnan Sasikiran (3.5) also signed peace with Iranian GM Ghaem Maghami (3.5).
Teenager G Rohit (3) of India shocked Bangladesh GM Zia Ur Rehman (2) in a marathon game arising out of modern defence while R B Ramesh of India outwitted Uzbekh GM T Vakhidov in French defence.
Women's GM S Vijayalaxmi of India defeated compatriot International Women Master Nisha Mohota.
Another IWM Bhagyashree Thipsay was held to a draw by Mumbai schoolboy Yashodhan Gogte in Sicilian defence while Zheng Peng Xiang (3.5) of China beat G B Prakash (2.5) of India.
S S Ganguly (2.5) of India drew with countryman Saptars Roychowdhury (2.5).