Carlsen tilted the scales in his favour with two consecutive wins in the fifth and sixth games of the 12-round world championship being played in Anand's home city of Chennai after the first four games were drawn.
The 22-year-old Norwegian, the current world number one and pre-event favourite, needs two wins and a draw in the remaining six games to seal the title held by Anand since 2007.
With one point gained for a win and half a point for a draw, the pressure is on Anand as even five draws in the rest of the match will enable Carlsen reach the winning tally of 6.5 points.
If points are equal after the 12th game on , the match will be decided by a tie-break or sudden-death on .
"I wanted to capitalise on my victory in the fifth game and so pressed foranother win in the sixth," Carlsen told reporters after winning the sixth round late .
"I am obviously in a good mood now. With six games to go, it is a healthy lead."
Anand, who at 43 is 21 years older than his rival, conceded it may need a miraculous turnaround to keep his chances alive.
"Losing the sixth game was a heavy blow, I won't pretend otherwise," the Indian wizard said. "I have just got to carry on. He has taken his chances, I have also got to do that."
Indian chess experts held out little hope for their compatriot with grandmaster Parimarjan Negi saying: "It will be very hard for him to come back now."
The total prize fund for the title clash is about $2.24 million with the winner getting 60 percent and the loser taking home the rest.
Anand, one of the most popular sports figures in cricket-mad India, and his opponent have enjoyed a remarkably similar rise in their careers from an early age.
Anand became an international master at 15, was crowned Indian champion at 16, won the world junior title at 17 and became the country's first grandmaster at 18.
Carlsen turned grandmaster at 13 and in 2010, aged 19, he became the youngest player in history to be ranked world number one. He won the Candidates Tournament this year to earn the right to challenge Anand.
Anand, who is based in Spain with his wife and young son, trails the challenger by a whopping 95 rating points and his world ranking has tumbled from number one to eight.