What about Garcia vs Ivkov, Havana 1965?
Ivkov had been on a meteoric rise... from World Junior Champion and Yugoslav National Champion, he had won a spot in the 1965 Candidates Matches by his success in the 1964 Interzonal. In the Capablanca Memorial in Havana, he defeated both (future World Champion) Bobby Fischer and (World Champion) Vasily Smyslov in their individual games.
Leading the tournament by half a point with only two rounds to go, GM Ivkov is the exchange and three Pawns up against the tail-ender. All he needs to do is make a few more moves to reach the move 40 time control.
Check out his 36th move, 36. ... d3.
http://www.chessgames.com/perl/chessgame?gid=1063717
One of the most ghastly blunders on record.
It destroyed Ivkov. He was completely demoralized by the disaster, and never reached the Candidates again.
I was wondering what was the top blunders in chess history
So here are some blunders