Anand shocked by Caruana
The loss, coming after a spate of three draws from the first three games, cost Anand quite dearly as from his joint lead, the Indian was pushed to the last spot.
The other game of the four-player double round-robin tournament between Vladimir Kramnik of Russia and Boris Gelfand of Israel ended in a draw in spite of a tough fight.
With just two rounds remaining, Caruana emerged as the sole leader with 2.5 points, a half point ahead of Kramnik and Gelfand while Anand on 1.5 point is currently at the bottom of the tables.
Anand's main chances now depend upon his final white game against Kramnik in the last round. The tide seems to have turned heavily in favour of Caruana, who finished second behind Anand in the just concluded Grenke Chess Classic.
Playing white, Anand faced the Moller variation in the Ruy Lopez and yet again Caruana came up with another opening idea and equalised successfully.
The Italian is fast turning into a player to follow when it comes to creating new ideas in a chess opening, every now and then coming out with some exemplary new ideas.
The middle game remained complicated but, understandably, Anand was playing for a win and went on pushing for an advantage that was not forthcoming.
As it happened, the world champion sacrificed a rook for a minor piece and apparently had decent compensation but his position worsened as the game progressed.