FC Steaua Bucureşti will defend a narrow advantage at Stamford Bridge in a week's time after Raul Rusescu's first-half penalty and a wholehearted performance put the 2012 UEFA Champions League winners on the back foot in Bucharest.
Rusescu drilled home a 34th-minute spot kick after he had been impeded by Ryan Bertrand while attempting a header from Iasmin Latovlevici's clever cross. The 24-year-old deserved that reward for an imposing display of muscular centre-forward prowess, his partnership with Alexandru Chipciu giving John Terry and David Luiz little respite in this round of 16 opener.
Backed by a passionate crowd, Steaua were at the London side's throats from the first whistle, contesting every ball. Hunting in packs, they did not allow Chelsea time to find any fluidity and consequently enjoyed the better of the first half. Indeed, a shooting chance fell Mihai Doru Pintilii's way as early as the sixth minute, but the angle was against him. When Chelsea responded, Branislav Ivanović headed wide from a Frank Lampard corner.
With Pintilii buzzing impressively in the central acres and Latovlevici ever-ready to add power and speed down the left, there was much to keep the home fans on the edge of their seats. They were good value for their breakthrough goal, yet it was so nearly cancelled out within two minutes when Yossi Benayoun swapped passes with Eden Hazard. The Israeli midfielder's shot was scuffed and Ciprian Tătăruşanu was able to make the stop.
Chelsea fought hard to try and restore parity ahead of the second leg. That invited Steaua to hit them on the counter and Cristian Tănase was not far wide on the volley. At the other end, an incisive pass found Fernando Torres well-placed inside the penalty area, but instead of going for goal he tried to lay the ball off to a colleague. Towards the finish, Marko Marin demanded a save from Tătăruşanu, while Luiz flashed a free-kick just too high.