The Cup holders were made to work hard by a Middlesbrough side full of endeavor, but quality goals from Ramires and Victor Moses in the second half proved to be the difference in the tie.
After a relentless schedule, manager Rafael Benitez named a side featuring eight changes for the trip to the Championship club. Although captain John Terry returned in the heart of the defense, the second-string nature of the lineup was encapsulated by first-starts of the campaign for Paulo Ferreira and Yossi Benayoun.
Middlesbrough will perhaps be content to be able to focus on their promotion challenge, but despite a poor recent record of seven defeats in their last nine matches, they acquitted themselves well early on.
Although Chelsea came close to an early breakthrough as Oscar’s shot was well blocked, the home side soon threatened with a header from forward Scott McDonald that just missed the target. Benitez went into the break with plenty to ponder as Middlesbrough winger Mustapha Carayol struck a shot from outside the box that Petr Cech couldn’t hold and Terry had to clear.
The visitors responded and came out for the second half with renewed vigor and took just six minutes to go in front.
Benayoun laid the ball back to Ramires 20 yards out and the Brazilian took a touch before curling a fine effort past Jason Steele with the aid of a slight deflection off of Fernando Torres.
With 17 minutes remaining Chelsea made the result safe. Eden Hazard provided an injection of quality off the bench and it was his fine change of pace that created the opening as he exchanged passes with Oscar on the edge of the box to get behind the back line before unselfishly squaring the ball for Moses to tap home and secure a trip to Old Trafford.