"It is certainly the toughest match I have ever played. I can't recall another experience like this," said the Indian ace, who won by a point: 6.5 - 5.5 to retain the crown he won in 2008.
"In the morning, when I woke up, we had no idea who was going to win, because even in the closest match it wasn't like one player was dominating and therefore I knew it was going to come down to the question of whose nerve held up and I am really relieved and glad that it was me," he added.
Anand said Topalov was one of the toughest opponents he's played and found it difficult to adapt against the Bulgarian.
"Since morning I wasn't thinking about any record. I was thinking just about staying alive. It was a bit difficult to adapt. Definitely, he is an incredibly tough opponent to have prevailed over this night. Honestly, I had no idea how it is going to shape up," he said.
Anand held the FIDE World Chess Championship from 2000 to 2002, at a time when the world title was split. The 40-year-old went on to become the undisputed World champion in 2007 and defended his title against Russian Vladimir Kramnik [ Images ] in 2008, thereby becoming the first player in chess history to win the world title in three different formats: knock-out, tournament and match.