The Blues registered a nervy 2-1 win over the Portuguese side at Stamford Bridge to seal a 3-1 aggregate victory and set up a semi-final with holders Barca later this month.
Chelsea doubled their aggregate advantage when Frank Lampard scored a 21st-minute penalty and their grip on the game tightened five minutes before half-time when Benfica skipper Maxi Pereira was sent off for a second yellow card after a lunge.
Javi Garcia headed in from close range on 85 minutes to prompt an awkward finale for the Londoners before Raul Meireles struck in stoppage time.
"As I said yesterday in the press conference, we expected a difficult game, a hard game, and that proved to be it exactly," he said.
"We probably made it a little bit more difficult for ourselves by not scoring a second goal, especially in that second half with all those chances. That kept them alive and (gave them) hope that they would score a goal and still be in it.
"They moved the ball around very nicely. We didn't quite keep possession enough as we'd have liked to with the extra man.
"I think the team wasn't as sparkling as we were hoping it would be. Maybe they were a bit tired, but we're pleased to have won the game and gone through. We deserved it over the two legs."
Asked about next opponents Barca, who Chelsea host in the last-four first leg on April 18, the Italian said: "It will be exciting to play two games against probably one of the best teams in the world.
"We will find a strategy that will suit our players and our team to face Barcelona.
"I think it will be a combination (of playing to our strengths and attempting to cancel out their players).
"They obviously have some individual players that are a big threat and very dangerous, but we also have to play our game and play to our strengths."
Benfica coach Jorge Jesus said: "We've been the best team in Lisbon and London and even though we played most of the match with 10 men tonight, we made Chelsea look ordinary.
"We pushed them back into the final third and after coming back to 1-1 we nearly scored with a couple of really good chances, but in the end suffered on the last counter-attack and were finally beaten.
"But we go out as the better team with our heads held high. Of course it is frustrating to lose but we weren't helped by some poor refereeing decisions either."
Chelsea have now reached the semi-final for the sixth time in the last nine seasons.
However, they have made only one final and have never won the competition.