The first chance of the half was created by the visitors in the 10th minute. The ball fell to captain Grant Holt on the edge of the area, but his powerful strike was saved by Paul Robinson in the home goal.
Norwich continued to create chances and Robinson had to be alert again to turn a long-range strike from Jonny Howson over the crossbar in the 23rd minute.
Blackburn's first meaningful effort on goal almost broke the deadlock. Junior Hoilett's cross was headed across goal by Morten Gamst Pedersen for Yakubu. However, the Nigerian's acrobatic effort struck the post before being cleared to safety.
The home side did not have to wait too long though to take the lead. Pedersen crossed to the back post for Formica, who guided the ball beyond the reach of John Ruddy in the away goal with four minutes of the half remaining.