After allowing an easy draw as white, it was Anand's turn to fight with the black pieces and the Indian ace took his chances when Giri ventured into troubled waters.
It was a double Fianchetto by Giri in the opening and the Dutchman allowed Anand to come up with an exchange sacrifice to get dangerous passed pawns on the queen side.
"Today I played a horrible game," said Giri. "I did everything to lose, but may be just not enough."
It turned out to be another tough day for world champion Magnus Carlsen as he lost his second straight game in a row against Fabiano Caruana of Italy.
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After losing on time against Bulgarian Veselin Topalov from a winning position, Carlsen could not match the deep preparation and dominating play of Caruana out of a Berlin defense game. The Italian was at his best in finding just the right resources and cruised home in the endgame.
Veselin Topalov thought he was "pushing for more" against Hikaru Nakamura of United States but the latter wriggled out with his trademark counter-active chess.