The Spaniard scored his eighth goal of the Premier League season in the Blues' comfortable victory.
Diego Costa scored his eighth goal in six Premier League games as Chelsea coasted to a 3-0 victory over Aston Villa at Stamford Bridge.
Costa has been nursing a hamstring problem, but there were no signs of an injury as he continued his outstanding start to his Chelsea career by finding the back of the net with a towering second-half header Saturday.
Oscar opened the scoring early in the first half with his second goal in as many games and that set the tone, as Jose Mourinho's league leader maintained its fine early-season form with a deserved win.
Costa doubled the lead just before the hour-mark and Willian added the third with a tap-in, his first goal of the season, to round off another impressive display from free-scoring Chelsea, which has now notched 19 goals in its first six top-flight games.
The London club suffered a costly 1-0 defeat at Aston Villa when the two sides last met back in March, which dealt a major blow to Chelsea's title hopes, but it gained revenge as Paul Lambert's men failed to recover from Oscar's early strike.
Villa has now suffered back-to-back defeats after losing its unbeaten record against Arsenal last weekend.
Ramires was ruled out with a muscular injury, so Oscar was given the nod to replace him in the only change to the side that drew 1-1 at Manchester City on Sunday.
Nathan Baker and Ashley Westwood returned to the Villa side after recovering from a virus that kept them out of last Saturday's defeat against Arsenal, so Ciaran Clark and Carlos Sanchez dropped to the bench.
Chelsea was indebted to John Terry after only six minutes, when the he got on the end of Aly Cissokho's inviting cross with a great defensive header as Kieran Richardson charged into the 6-yard box behind him.
Villa was caught out just a minute later, though, when two of the home side's Brazil internationals combined to put Chelsea in front.
Willian raced away down the inside right and, after his shot was palmed straight back to him by Brad Guzan, the former Anzhi man cut the ball back to the onrushing Oscar to side-foot home despite the best efforts of Alan Hutton.
The visitors responded and Cissokho fired just wide with his right foot after Chelsea failed to deal with a corner from the right.
Chelsea was dominant and Willian laid on another chance when he picked out Costa with a cross, but the Brazil-born striker's powerful header was saved by Guzan.
The visitors showed little ambition going forward in the first half, but Fabian Delph gave Chelsea a warning just after halftime when he evaded a couple of challenges before unleashing a venomous left-footed strike from long range that flashed past the far post.
Baker rose highest to meet a free kick, but headed onto the roof of the net and Costa ought to have made him pay when he failed to get a good contact on his header after Branislav Ivanovic picked him out.
The former Atletico Madrid man was not to be denied 59 minutes in, though, when he got in front of his marker to head home a Cesar Azpilicueta cross from 8 yards out to round off a slick Chelsea move.
Oscar must have thought he had his second when he poked the ball beyond Guzan, but Cissokho raced back to clear just before it could cross the line.
Willian then got his name on the score sheet, converting from point-blank range after Costa's shot was saved by Guzan 11 minutes from time.