A 75th-minute strike from Salomon Kalou gave Chelsea a hard-fought win at the Stadium of Light after Benfica had carved out the better chances but failed to land the knockout blow against their Premier League opponents.
The result also represented vindication for interim Chelsea manager Roberto Di Matteo, who had taken a huge gamble by surprisingly omitting veterans Frank Lampard, Didier Drogba and Michael Essien from his starting line-up.
The win puts Chelsea firmly on course to reach their sixth Champions League semi-final in nine seasons heading into next week's return leg.
"It's terrific, you couldn't have hoped for a better result," a delighted Di Matteo said.
"I thought we looked good defensively. For 90 minutes we had to run and tackle, and I had to select a team that had the energy to compete.
"Nothing is over. There is still another 90 minutes to play. But we will have home advantage and we will try and qualify."
Goalscorer Kalou said Chelsea's united dressing room had made victory possible.
"We played as a team and when you play as a team it makes it easier to win," he said. "Any goal is important. I'm just happy to have scored."
A subdued first half saw neither side manage to get a grip on the game, with Chelsea failing to get a shot on target until Raul Meireles tested Artur with a fierce low strike on 40 minutes.
Benfica were scarcely much better, although the movement of Oscar Cardozo and Nicolas Gaitan had hinted at the home side's attacking threat.
Cardozo had been the first to draw a save from Petr Cech on 11 minutes, but his tame header from Gaitan's cross on the left was comfortably gathered by the Chelsea goalkeeper.
Gaitan was back in the thick of it on 20 minutes, threatening the Chelsea area following a quick free-kick only to shoot wide after getting goal-side of John Terry.
Chelsea forays into Benfica territory were few and far between, with Fernando Torres's high and wide shot on 22 minutes the sum total of their early efforts.
Benfica had one of the few attempts on goal in the 33rd minute when Bruno Cesar cut in from the right and shot, but again Cech was equal to the challenge, collecting the effort with relative ease.
It looked as if Chelsea were going to go an entire half without testing the Benfica goal before Meireles finally found his range five minutes before the break.
Ashley Cole picked out the Portuguese midfielder in space near the edge of the area and he unleashed a powerful low drive that Artur parried behind.
Benfica came out for the second half with a far greater sense of purpose and threatened the Chelsea goal twice in the opening five minutes.
Only a desperate goal-line clearance from David Luiz prevented a Benfica goal on 48 minutes, the Brazilian defender blocking Cardozo's thumping shot from the edge of the area.
Two minutes later Benfica were back on the attack, Pablo Aimar jinking forward and feeding Cesar, who tested Cech with a dipping long-range shot.
Yet Chelsea also had a golden opportunity to open the scoring on 53 minutes.
Torres curled in an inviting cross from the left but the unmarked Kalou could only head over from six yards with the goal begging.
Benfica remained in the ascendancy but Chelsea again were given a clear chance on goal on the 60-minute mark.
A long clearance by Cech somehow eluded all of Benfica's defence and found Juan Mata, who touched past Artur to go through on goal. The acute angle proved too much for the Spaniard, however, and his shot cannoned back off the upright.
Yet Benfica continued to look the likeliest to score, and Axel Witsel's deflected long-range shot flew just over on 65 minutes after a desperate block from John Terry.
A brilliant Cech save from Jardel's powerful close-range header then denied Benfica on 67 minutes as Chelsea survived again.
But with 15 minutes to go Chelsea struck with a goal from nothing.
Ramires, whose pace down the right had troubled Benfica all evening, once again surged down the flank into space.
The Brazilian midfielder fed Torres, who looked up and picked out Kalou, who jabbed home from close range to stun the Stadium of Light into silence.
Benfica never recovered their rhythm and Chelsea held on as the Portuguese side were beaten at home in Europe for the first time this season.
Source: AFP
Source: AFP