The result sends The Citizens back to the top of the table once again of goal difference, after Arsenal's 4-1 demolition of Sunderland earlier on Saturday.
Tony Pulis made two changes from the side that lost 2-1 at Anfield last weekend. Jonny Evans returned from suspension to - in turn - replace the banned Claudio Yacob in midfield. Chris Brunt made his first start in eight months, as Matt Phillips dropped to the bench.
The Citizens made three changes with Nicolas Otamendi preferred to Vincent Kompany in central defence. With Leroy Sané ruled out, Fernando filled in at right-back. In Pep Guardiola's only other change, Kevin de Bruyne was only fit enough for the bench as Nolito was recalled.
With Manchester City desperate to dig the way out a slun, the visitors raced out of the traps from the kick off. Ben Foster was forced into early saves from Raheem Sterling twice in the opening 15 minutes.
Midfielder Nolito had already served a three match ban for headbutting AFC Bournemouth's Adam Smith last month. The Spaniard was fortunate in the extreme to not see red again after an altercation with Craig Dawson. Referee Lee Mason saw fit to only caution the City man.
Aguero double breaks deadlock
After John Stones missed a chance from six yards out - side-footing wide of the Baggies' net - Guardiola's men finally opened the scoring in the 18th minute. Following clever play from Ilkay Gündogan, the German slipped a ball through to Kun Agüero. The Argentine steadied himself and slipped the ball past Foster, to score his first goal league goal in four games.
Fernandinho shied from long-range as City sought a second, before the class of Agüero once again shone. With the ball bobbling around between Nolito and David Silva, the Argentine picked up the ball, cut outside Gareth McAuley and lashed a curling drive into the top-corner, doubling City's advantage.
The visitors coasted into a 2-0 lead as the referee blew for half-time.
Baggies sense opening in second period
The Baggies made a double change just five minutes after the break, as the hosts sniffed an way back into the contest. The injection of both Jonathan Leko and James Morrison gave West Brom momentum, as the game opened up.
With the much maligned Claudio Bravo under scrutiny, the Chilean stopper survived a scare when racing out to intercept a ball over his defence, again misjudged his clearance, but Salamon Rondon could only head wide.
The Venezuelan was involved again as just after the hour mark, James McClean raced down the left and slotted a ball across the Manchester City area, but Rondon couldn't quite sort his feet out and flicked the ball wide of Bravo's goal.
Gundogan seals the three points
As West Brom pushed forward, they were caught out once more by Guardiola's men. Fernandinho picked the ball up on the edge of the area and found Aguero. With his tail up, the forward ran across the Baggies defence, and found Gundogan who added a third to the tally.
Late on, the German scored his second via substitute Kevin de Bruyne's pass, as Manchester City cruised to a 4-0 win and overtake Arsenal to go top once more.