Grandmaster Viswanathan Anand said by winning his fourth World Chess Championship title early this month he has proved critics who accused him of lacking in killer instinct wrong.

Anand retained his World Chess Championship title after beating Bulgarian Veselin Topalov in a nerve-wrecking 12th and final game on May 11 in Sophia and the Chennai-born Indian said the triumph was a special one.

"Generally people accuse me of lack of nerves or killer instinct. My nerves worked better. I defended the third title in a row and that is very special," he told reporters.

Anand said the contest against Topalov was the toughest of the World Championship matches he played and his Bulgarian opponent was an incredibly tenacious fighter.

"It was the toughest that I played. Every game was intense and hard fought. We almost never finished a game under four hours. It was exceptionally tense and nerve-wracking," he said.

"I knew that any way he was not going to offer draw (12th game). For the first time we did not speak to each other during the match. Only at the end of the game he spoke," he said.

"I generally had the edge over him (Topalov). Even there the dominance was not clear at all. That perhaps makes the joys of pulling it off in the end even greater," he added.

Comparing his latest world title with the earlier three, Anand said, "It was tough on the chess board and off it. In general, I guess this is how the match is supposed to be.

"It was just that in the earlier championships I suddenly built up a huge lead. But this match went the whole length. In that sense this championship was the sternest test that I ever faced," he added.

There were many firsts en-route to Anand's World Championship title.

It was the first time he travelled by bus to the Championship because of the volcanic ash that emanated from Ireland. It was the first match between "non-Soviets" since 1921.

It was the first time a player defended his title after losing the first game.

"This is incidentally the first World Championship match that I played full length. Every other match finished actually ahead of schedule," Anand said.

As for the support he received from Gary Kasparov and Vladimir Kramnik during the Championship, Anand said it gave him a boost.

"It is difficult to say very precisely. There were many difficult moments in the match, a lot of tense moments, suddenly you get a phone call from Gary or Kramnik, and it definitely cheered me up a lot. This is the first time that I received this kind of help," he said.

Asked which of the matches in the Championship were tough, Anand pointed out four games.

"I should have drawn the eighth game. At the end of a long defence I mixed up and forgot a move that I had seen earlier. I am not trying to take credit away, but if you press your opponent all the time, a mistake will happen.

"But, still, that is the tough way to lose a game," he added.

"In the 12th game I decided to change my strategy a bit. I had played an opening the queens-gambit declined that I had not intended to before the match. It gave me a psychological boost and it worked extremely well with the black pieces," he said.

On Russian domination of World Championship titles, Anand said, "I would say that their dominance was not what it used to be. I doubt that any country will dominate like the Soviet Union."

Anand said he would probably take a month's rest.

"Two years can fly between matches and from July I have to start working intensely and do some training. I enjoy working on chess and finding new things," he said.

He said he needs to keep changing his strategy constantly.

"First of all, chess does not stand still. You have to work much harder," he said.

He explained that was the reason that he would start working again pretty soon.

"I have the experience from the last time like after the match in Bonn. I understood that how little time I had to prepare for the World championship," he added.

On keeping himself relaxed, Anand said his seconds knew about everything that was important when it came to chess.

His wife took care of non-chess-related aspects in the match.

''It is a very nice bubble to be in. When you come out of it, some things make you wonder how long you have been away like a time warp," he added.

He said the game of chess is also recovering from the split federation for 13 years and so on.

For the first time, there is three "stable" World Championships and he is happy to be part of that.

Anand said it is inevitable that India will have more World champions.

"Many of the Indians are waiting for breakthrough moments. It can come anytime. I think you need to keep your faith and keep working.

"I would also say that we are expanding the pool of people through NIIT Mind Champions Academy, who not only enjoy chess but play seriously to be professionals in later life. It is inevitable that we will have more world champions," he said.