Stunned 2-1 by Basel at Stamford Bridge in their opening game, Chelsea were eager to make up for lost time and the Europa League champions never looked in trouble beneath the closed roof of Bucharest's Arena Nationala.
Ramires broke the deadlock in the 20th minute, with hapless Steaua right-back Daniel Georgievski putting through his own goal on the verge of half-time.
Ramires added a third early in the second period, before Frank Lampard's low shot sealed victory in the 90th minute.
"I think the performance was very solid, from the first minute," Chelsea manager Jose Mourinho told Sky Sports.
"We kept always the control of the game and the result, and I think we played good football, but also with intelligence and maturity.
"I think we are going to do it. I think we are going to qualify. This result today is important, because if you don't win, you are a bit under pressure."
The one false note for the visitors, beaten on this ground en route to success in the Europa League last season, was an injury to Fernando Torres, who left the fray after hurting his knee in the 11th minute.
Mourinho, though, said he did not think the injury was as severe as the one that recently saw Chelsea's Dutch midfielder Marco van Ginkel ruled out for around six months.
"We have to wait. Tomorrow (Wednesday) we will have the scans and we will see what happens," he said.
"I hope it's not one more dramatic like Van Ginkel. Doc (Paco) Biosca says not to be so worried, because it will not be a Van Ginkel situation."
Schalke's 1-0 win at Basel in the other Group E game leaves them three points above Chelsea at the summit ahead of back-to-back games between the sides later this month and in early November.
Mourinho brought Andre Schurrle and Juan Mata into the team that drew 1-1 at Tottenham Hotspur on Saturday and the Spaniard almost teed up Schurrle for an early opener, but Iasmin Latovlevici blocked.
The visitors' purposeful start threatened to be upset by the premature departure of Torres, but his replacement, Samuel Eto'o, was quick to make a telling contribution.
Schurrle sped past Georgievski on the Chelsea left and centred for Eto'o, who mishit his shot but saw the bobbling ball prodded home by the alert Ramires.
Schurrle blazed over and Mata had a shot comfortably saved by goalkeeper Ciprian Tatarusanu, before the blundering Georgievski inadvertently doubled Chelsea's lead in the 44th minute.
Eto'o was again the catalyst, surging onto Mata's pass, cutting inside Latovlevici and dispatching a shot that Tatarusanu parried, only for the ball to rebound into the net off the shin of the onrushing Georgievski.
Chelsea put the game to bed 10 minutes into the second half, following another strong burst down the left flank by Schurrle.
His centre found Oscar, who in turn laid the ball off for Ramires to rattle a shot between Tatarusanu and his left-hand upright.
Mourinho's delight was evident as he congratulated Schurrle with a touchline hug.
Moments later, Mata struck the post from a delightful Oscar back-heel, while Schurrle went close to crowing his display with a goal by curling a shot fractionally wide of the far post.
Steaua had their moments, however, with goalkeeper Petr Cech obliged to tip a feathery chip from Cristian Tanase over the crossbar and block from Nicolae Stanciu, who lashed the rebound over.
Lampard prevented Lucian Filip from claiming a late consolation with a sharp block and then completed the scoring at the death by sweeping home a lay-off from substitute Willian.