A dour performance from the Blues sees them head to Stamford Bridge with a narrow 1-0 deficit thanks to a first-half spot kick that was given away by Ryan Bertrand.
In the first-ever meeting between the two sides, Raul Rucescu scored what the winner as he converted a first-half penalty after being brought down by Ryan Bertrand.
Chelsea offered very little in response and goes into the second leg at Stamford Bridge knowing the tie is still finely poised, though the team's dour performance will hardly leave the players brimming with confidence.
Benitez made five changes from the Blues' 1-0 win over West Brom on Saturday, with skipper John Terry, Yossi Benayoun, Bertrand and John Obi Mikel all starting, while Fernando Torres was selected to lead the line.
The home side kept Cristian Tanase in the starting lineup despite his sending off during the team's win over Gaz Metan, although striker Stefan Nikolic missed out with a knee injury.
A tentative opening period saw the visitors sit back and soak up what Steaua had to offer, with an initially subdued atmosphere hardly providing either side with encouragement early on.
The first moment of inspiration came on the quarter of an hour mark when Torres showed skill and determination to beat the home left back. Nothing came of it as his follow up sent the ball out of play – but at least it was a glimpse of the Spaniard of old.
Torres was at it again 15 minutes later, pressuring the Steaua defense to win a corner, but it was duly wasted.
There was simply no dynamism in Chelsea's play. After the highs of last May's Champions League victory, no one would blame those present in Munich for asking if this was the same club as the one that lifted Europe's top prize.
It got worse for the Blues minutes later as Bertrand conceded a penalty after fouling Rucescu inside the box. The decision was debatable but the referee’s word was final and Bertrand saw yellow. Rucescu took the spot kick and, showing no hesitation, the Romanian slammed the ball past Petr Cech straight into the bottom left corner.
Chelsea hit back as Benayoun forced a save from Ciprian Tatarusanu on 40 minutes – but it said a lot that it was the team's first meaningful shot on goal of the encounter.
It was more of the same after the break. The home side held the ball well and, aside from the odd surging run from Eden Hazard, the Chelsea was nonexistent.
On 63 minutes, Frank Lampard dinked a pass through to Torres in an attempt to create something, but it was to no avail. Benitez knew there was only one man who could inject the required spark and sent on Juan Mata. But the Spaniard’s introduction changed little.
Hazard flashed a volley over after 73 minutes, while Marko Marin came close at the near post 10 minutes later, yet the home side held on to secure its 17th win in 19 home games this season.