Carlsen misplayed an even end game and was defeated by Keymer, a Grandmaster with a FIDE ranking of number 34 in the world, in the day’s stand out result in the open category.

After a mistake on his 36^th move Carlsen lost a pawn, with Keymer going on to complete victory after smoothly converting his extra pawn in a knights end game.

Elsewhere in the open draw there were four other winners including Alexey Sarana, who now represents Serbia, defeating Wesley So of the United States.

European champion Sarana took advantage of an error by So, finishing off his opponent with a series of impressive moves.

The day’s other winners in the open draw were India’s Vidit Santosh Gujrathi, who beat France’s Etienne Bacrot, Sweden’s Nils Grandelius, who overcame Jaime Santos Latasa of Spain and Berenc Ferkes of Hungary, who beat Ruslan Ponomariov of Ukraine.

In the women’s draw only one of the day’s fourth-round matches ended with a win, as Georgian Grandmaster Bella Khotenashvili defeated India’s top-ranked female chess player Humpy Koneru.

An early mistake by Koneru put her in a weak position that she was unable to recover from, forcing her to concede defeat on the 42^nd move.

Among the drawn matches were China’s reigning women’s world champion Ju Wenjun against Germany’s Elisabeth Paehtz and a meeting of two sisters from Ukraine Anna and Mariya Muzychuk.

Game two in fourth-round matches in the open and women’s draws are due to be played tomorrow, with any matches still level overall then going to tiebreak matches on Friday (August 11) if required to decide a winner.