In a game that it controlled from start to finish, the home side opened the proceedings courtesy of a well-worked set-piece as, after Luiz headed an Oscar delivery back across the face of goal, the former West Ham man was there to put the Blues deservedly ahead.
Chelsea continued to control the game but, despite proving unable to further capitalize on its dominance, it saw out the game fairly comfortably, in spite of a couple of adept late saves from the largely untested Petr Cech.
Benitez, as expected, made wholesale changes from the rotated side that overcame Middlesbrough in the FA Cup on Wednesday, as Cesar Azpilicueta, David Luiz, Ashley Cole, Frank Lampard, Eden Hazard, Juan Mata and Demba Ba all returned to the starting eleven.
The away side, meanwhile, made a couple of enforced changes from the side that beat Sunderland 2-1 last Saturday as, with Romelu Lukaku unable to play against his parent club and captain Chris Brunt injured, Marc-Antoine Fortune and Graham Dorrans stepped into the starting eleven.
Chelsea had the better of the opening proceedings and were almost ahead after just three minutes, as, after Ba put in a good delivery from the right, Oscar almost converted, only to be denied by a smart Foster save.
Aside from a long-range Steven Reid free kick that Petr Cech tipped over, the home side managed to control the early stages as Oscar and Ba both missed opportunities to break the deadlock within the opening half-hour.
Eventually though, Chelsea's goal arrived and it was courtesy of a cleverly-worked short corner. After a Luiz's free kick was tipped adeptly wide by Foster, Oscar received the ball short from the ensuing set piece and whipped a ball towards the back post. Luiz was there to head the ball back across the goal, finding Ba on the edge of the six yard box to put the home side deservedly ahead after 28 minutes.
After seeing out the remainder of a testing first half, the Baggies' second half continued in much the same vein as Chelsea absolutely dominated the opening fifteen minutes, albeit without really testing Foster.
The game took a contentious turn with an hour gone as there were vehement claims for a penalty after Olsson appeared to bring down Hazard in the area; the referee deemed it a fair challenge though and Chelsea continued to search for a potentially decisive second goal.
Oscar went closest to putting his side further ahead with around fifteen minutes remaining as he was denied twice in quick succession by Foster as the goalkeeper first saved well from the Brazilian's volley, before then tipping wide from his low strike.
With the home side proving unable to further capitalize on its dominance, the Baggies started to threaten with ten minutes left on the clock as Cech was tested twice in a matter of minutes as substitute Peter Odemwingie forced him to tip over from a free-kick, before he then palmed a goalbound Azpilicueta header over and away.