Young Bharat Subramaniyam's good run came to a halt after Azerbaijan Grandmaster Rauf Mamedov defeated the 13-year-old Indian in the fifth round of the Aeroflot Open chess tournament here.
The 51-move win late on Sunday enabled Mamedov to become the sole leader with 4.5 points.
Mamedov used his experience to beat the Indian, who had posted two memorable wins over GMs in the first four rounds.
Subramaniyam had in the earlier rounds beaten Chinese Grandmaster Jiancho Zhou and Gabriel Sargissian, the second-seed.
Armenian GM Manuel Petrosyan is in second place with four points after scoring a win over India's S P Sethuraman (now on 3 points).
Subramaniyam and compatriot B Adhiban and Aravind Chithambaram, the national champion, are in joint third spot on 3.5 points with 13 others.
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In his fifth round game, Adhiban shared honours with Aleksej Aleksandrov while Chithambaram beat Vahap Sanal.
Meanwhile, talented young GM R Praagnanandhaa (Elo 2602) went down to lower-rated Russian GM Mikhail Antipov.
Top-seeded Russian Vladislav Artemiev moved to three points after sharing the point with Iran's Pouya Idani.
Important Results of Aeroflot Open 'A' Group 5th round: Rauf Mamedov (AZE) 4.5 beat Bharat Subramaniyam (IND) 3.5; S P Sethuraman (IND) 3 lost to Manuel Petrosyan (ARM) 4; B Adhiban (IND) 3.5 drew with Alekesej Aleksandrov (BLR) 3.5; Vladislav Artemiev (Russia) 3 drew with Pouya Idani 3.5.
R Praggnanandhaa (IND) 2.5 lost to Mikhail Antipov (RUS) 3.5; Vaibhav Suri (IND) 2.5 lost to Aleksandr Rakhmanov (RUS) 3.5; Boris Savchenko (RUS) 3.5 beat SL Narayanan (IND) 2.5; Aravindh Chithambaram (IND) 3.5 beat Vahap Sanal (TUR) 2.5; Vadim Zvjagnisev (RUS) 3.5 beat M Pranesh (IND) 2.5.