Celestine Babayaro's first goal in three years broke the spirit of brave Middlesbrough and kept the Londoners on course for a tilt at the Premiership title.
Two minutes in to the second half, Gianfranco Zola split the Middlesbrough defence with a wonderful reverse pass. He bisected the defence and played in Babayaro, who cut in front of Geremi, into the penalty area and blasted a right-footer with such pace that goalkeeper Mark Schwarzer has no chance.
Up to that point, Boro, who had the best defence in the Premiership more than contained Chelsea who had the third best defence. Chelsea now have not conceded a goal in five matches.
"When a team gets past us, they still have to get through Cudicini," beamed Chelsea coach Claudio Ranieri.
"It was a fantastic game," he added. "I'm so happy to have won, but would not have been surprised had we drawn or even lost. Middlesbrough certainly deserved to get something from the match.
"But if we are to get into the top four, these are games we have to win." Zola may have being the star, but Chelsea keeper Claudio Cudicini was magnificent to hold off Boro.
In the first half, the Italian make two excellent stops against livewire Massimo Maccarone.
In the second, with Alen Boksic just on the pitch, he produced another brace of saves. Late into injury time, he once again smothered a blistering shot from Joseph-Desire Job.
"We are a very hard team to beat," an upbeat Steve McClaren said. The Boro boss was happy with his side's effort and commitment.
"I couldn't have asked for any more from the players. But we switched off just for a second, and it was the difference. Other than that, we were not in a real danger." Chelsea boss Ranieri has the greater chance of landing some silverware this season: "My target is to get into the top four places," he said. "I am an ambitious man, and my team and supporters are also ambitious.
"If we are still in third place after Christmas I'll be a very happy man."