Fernando Torres' three-month goal-drought continued as Chelsea missed the chance to close the gap on the Premier League leaders with a 0-0 draw at Premier League newboys Norwich on Saturday.
Chelsea enjoyed the better chances of a scrappy game at Carrow Road but were left frustrated as £50 million striker Torres drew a blank yet again.
The draw left Chelsea in fourth place, five points adrift of third-placed Tottenham, who face leaders Manchester City at Eastlands on Sunday.
Spanish star Torres, who has not scored for Chelsea since October, went close with an improvised first-half shot only to be denied by a brilliant diving save from Norwich goalkeeper John Ruddy.
The 27-year-old also spurned a glorious chance midway through the second-half, shooting agonisingly wide from seven yards after taking one touch too many from Jose Bosingwa's cross.
Ruddy was pressed into duty moments later, saving smartly at the near post from a Juan Mata shot after the Spaniard cut in from the left.
A miserable afternoon for Torres -- who has now not scored for 15 games -- ended in the 77th minute when Villas-Boas substituted his misfiring striker for Belgium international Romelu Lukaku.
Mata tested Ruddy again on 81 minutes, his shot and turn being parried just wide by the in-form Norwich goalkeeper, who was later named man-of-the-match.