World champion chess computer software program Deep Junior pounced on a glaring error by Garry Kasparov on Thursday to draw level with the Russian grandmaster halfway through their six-game match in New York.
Playing with the white pieces, the Azerbaijan-born Kasparov blundered with a rook move on his 32nd turn of the third game, allowing the machine to go two pawns up in material and establish a winning endgame.
"This was a time pressure move that is ridiculous by his high standards," US grandmaster Maurice Ashley said. "It makes the greatest player of all time look very human."
Kasparov's furious reaction at the board when he realised his mistake left no doubt he had betrayed himself after playing an enterprising game that appeared drawn even though the human player had less time on his clock.
The former world champion who is still ranked number one, shook his head vigorously, stared up at the ceiling and covered his face with his hands as the computer crunched out the win.
Kasparov resigned on the 36th move after three hours and 45 minutes because his position was about to become hopeless with three pawns and his queen to Deep Junior's five pawns and queen.
Kasparov, whose battles with the IBM supercomputer Deep Blue in 1996 and 1997 drew worldwide attention, has vowed to avenge his defeat to the machine six years ago, but now faces a tough psychological struggle for the remaining three games.
"Kasparov blundered... at that point the position was probably a draw," said US grandmaster Lev Alburt after watching the game at the New York Athletic Club.
The $1 million match billed the International Chess Federation Man v Machine World Championship' is tied at 1-1/2 points each with the fourth game scheduled for Sunday.
One point is awarded for a win and half a point for a draw. Kasparov won the first game last Sunday and Tuesday's second game was drawn.
The human programmers of the Israeli-built software program that runs on a PC were excited by the victory.
"Behind this is the accumulation of a lot of effort and this is the epitome of what we are doing," said programmer Shay Bushinsky, who along with fellow Israeli Amir Ban have worked on Deep Junior for 10 years. "Deep down in our hearts we are happy."
The games are being shown as they are played on the Web sites http://www.x3dworld.com and http://www.chessbase.com