Top seed Grandmaster Koneru Humpy bowed out of the Women's World Chess Championship after losing in the semi-final tie-breaker against Woman Grandmaster Ekaterina Kovalevskaya of Russia at City Chess complex in Elista.

Humpy lost 0.5-1.5 to Kovalevskaya on Tuesday despite being at advantage in all four games of the tie-break match, which was played after the Indian had won the second of the two-game semi-final.

In the tie-breaker, Humpy drew the second game after losing the first game despite having a stronghold with black pieces.

It was a Sicilian Dragon by transposition where Humpy, white, thoroughly confused her opponent and won a piece in the opening itself in the drawn game.

However, as the endgame surfaced, the 17-year-old pre-tournament favourite could not sustain the tremendous pressure and paved way for the Russian to get a theoretically drawn endgame that lasted till the 67th move.

Kovalevskaya did well to hold her position once she was out of real danger and after the exchange of queens took place, she retained her winning chances.

Humpy eventually saw a similar finish to that of her first loss, and was a rook down in the end. Kovalevskaya clinched the issue in 68 moves.

In the other semi-final, Grandmaster Antoaneta Stefanova of Bulgaria ousted former World Women champion Maia Chiburdanidze of Georgia.

Maia was earlier also restricted at the semi-final stage in the last World Championship in 2001 at Moscow against champion Zhu Chen of China.

Stefanova has so far had some resounding successes in this event and is now down to the finals against Kovalevskaya.

In her second game of the two-game semi-final, the Bulgarian gave an emphatic display to beat Chiburdanidze who did not handle her white pieces well enough.

The Georgian surprisingly opted for the irregular opening choice and her opponent, by the end of opening phase, found her pieces stranded on the wrong squares resulting in a loss of pawn.

Playing in copy-book fashion thereafter, Stefanova did well to keep Maia's forces in check on the king's wing and at the same time continued with the demolition act on the other flank that netted two more pawns.

To begin the end, Stefanova sacrificed her rook for a Bishop to let her pawns create havoc. Chiburdanidze efforts to make the impossible happen went in vain and she was forced to sign her ouster papers after 55 moves.

Earlier, Humpy, who suffered a shock defeat in the first game, bounced back superbly to push the match into tie-breaker.

After squandering a winning chance in the first game, the Indian was back to her basics and played the do-or-die second game with absolute concentration. She was also assisted by lady luck, according to experts.

It was a Bogo-Indian defence that gave Humpy, playing white, a tangible advantage and slowly she started exerting  pressure on the queenside after trading the queens in the early opening.

Though the queen-less middle game offered sufficient counterplay to Kovlevskaya, Humpy was instrumental in forcing the Russian to part with a pawn.

Thereafter, Kovalevskaya played quite well and had enough compensation for the lost material. But with the clock ticking away she committed a positional blunder on the 27th move that spelt her doom.

The wily Indian soon co-ordinated her pieces and easily won a second pawn that was part of the erroneous package offered by Kovaevskaya. Soon it was curtains for the Russian after further simplification took place. The game lasted 51 moves.

After levelling the scores at 1-1, Humpy looked absolutely relaxed and went to her room to prepare for the tie-breaker.