Top seed Grandmaster Koneru Humpy went down to Yifan Hao of China in what was perceived as the title match in the seventh round of IS Bank Ataturk Women Grand Prix event in Istanbul on Sunday.
Humpy, who had been trailing Yifan by a half point coming into this round could not withstand enormous pressure from her opponent and went down after putting up a good fight.
Humpy now stands third with five points and apart from winning her own games, will need a lot of luck to win the tournament.
For Yifan this was a decisive stride forward in her quest for the title here as she took her tally to 6.5 points out of a possible seven and is followed by compatriot Zhao Xue who added to the woes of Martha Baquero Fierro of Ecuador.
It was a Ruy Lopez wherein Humpy was gradually outdone playing black.
Yifan played imaginatively on both flanks and had things under control once the middle game surfaced. Humpy tried her counter play but it did not quite materilise as Yifan's attack on the king side proved dangerous.
The Chinese teenager gave up two minor pieces for a rook to build the pressure further and Humpy could not find the right defense.
In the final stages of the game Yifan's attack became unstoppable and she finished the game in style with a rook sacrifice bringing the black king out of its shelter and when the threat of checkmate became inevitable Humpy called it a day.
The game lasted 50 moves.
Elina Danielian of Armenia is the other player in contention for a podium finish with 4.5 points in her bag.
Zhao Xue exploited her slight advantage out of a Classical King's Indian in fine style. Martha could not find a proper defense in the endgame and lost in 56 moves.
After a stupendous start, this was Martha's third loss in a row and put her out of contention.
In other games of the day, former world champion Maia Chiburdanidze of Georgia defeated Zeinab Mamedjarova of Azerbaijan in a Queen pawn game where the former played white while Antoaneta Stefanova could not break the defenses of Shen Yang of China and had to sign peace.
French girl Marie Sebag was the other winner at the expense of Betul Cemre Yildiz of Turkey while Elina Danielian played out a draw with Pia Cramling of Sweden.