The spotlight was on new £49million man Raheem Sterling, but it was David Silva and Yaya Toure who stole the show to help ease City to three points.
Toure was influential in City's first two goals, first producing a shot which was flicked by Silva and then deflected off defender Craig Dawson on its way in, and the second a fine finish before the 25-minute mark
Vincent Kompany then completed a comfortable triumph for the visitors just before the hour.
City, and their old guard, were too strong for the Baggies, who saw Saido Berahino waste their best chance.
Sterling should have also marked his debut with a goal, but was denied by Boaz Myhill when clean through.
The 20-year-old started in support of Wilfried Bony, with Sergio Aguero on the bench, while Albion handed debuts to Rickie Lambert, James Chester and James McClean.
Albion's new £12million record buy Salomon Rondon was unveiled to the crowd hours after signing from Zenit St Petersburg, along with Arsenal loanee Serge Gnabry.
And the new boys would have watched in horror as City dismantled their hosts in the first half.
They had threatened without testing Myhill but deservedly took the lead after nine minutes with a goal which happened almost in slow motion.
Silva had already gone close as his cross shot found the waiting Jesus Navas at the far post and he teed up Toure on the edge of the box
The midfielder was gifted time to shoot and his mis-hit effort was flicked on by Silva before hitting the helpless Dawson and crawling across the line
City had settled and were toying with the Baggies, trying to find the perfect pass to carve them open.
Albion, in contrast, relied on hopeful long balls as Berahino and Lambert became increasingly isolated.
The visitors were in total control and they underlined their dominance in ruthless fashion after 24 minutes.
This time there was no doubt over the scorer as Toure swapped passes with Bony before unleashing an unstoppable effort into the top corner from 20 yards.
City kept Albion at bay until three minutes from half-time, when Berahino clipped over Joe Hart only to be ruled offside.
A minute before, though, Sterling should have marked his debut with a goal when Toure put him clean through, only for Myhill to save his low weak effort.
It would have ended the game but, instead, the hosts emerged for the second period with renewed belief.
First, Lambert's 30-yard free-kick whistled over before Berahino's tame finish fell to the under-worked Hart.
The striker should have done better and was left to rue the miss when City made it 3-0 on 59 minutes as Kompany glanced in Silva's corner with his shoulder.
The contest was over and the visitors had the luxury of bringing Aguero off the bench, while Samir Nasri also replaced Sterling.
Hart gathered James Morrison's header with 14 minutes left but there was no way back for the Baggies.
Aguero almost added a fourth with two minutes left, but his low six-yard effort was blocked by Myhill before the goalkeeper saved Aleksandar Kolarov's stoppage-time free-kick
TWEET OF THE MATCH
"A very impressive performance from Manchester City
Silva is different gravy!"
Gary Lineker purrs over another David Silva masterclass
https://twitter.com/GaryLineker/status/630843778094469121
RATINGS
West Brom
Boaz Myhill: 6 (out of 10)
James Chester: 6
Joleon Lescott: 6
Craig Dawson: 6
Chris Brunt: 6
James McClean: 5
Darren Fletcher: 6
James Morrison: 5
Craig Gardner: 5
Rickie Lambert: 5
Saido Berahino: 6
Substitutes:
Claudio Yacob: 5
Callum McManaman 5
Victor Anichebe 5
Manchester City
Joe Hart: 6
Bacary Sagna: 7
Vincent Kompany: 7
Eliaquim Mangala: 7
Aleksandar Kolarov 8
Yaya Toure 8
Fernandinho: 7
Jesus Navas: 7
David Silva 9
Raheem Sterling 7
Wilfried Bony: 7
Substitutes:
Sergio Aguero: 6
Samir Nasri: 6
Martin Demichelis 6
STAR PLAYER
David Silva
The midfielder was at the heart of everything the visitors did and was at his majestic best to pick West Brom apart
He flicked on Yaya Toure's shot in the opening goal and set up Vincent Kompany's header for City's third
Albion resorted to fouling the Spain international to stop him as he ran the game at The Hawthorns
MOMENT OF THE MATCH
Toure's strike to put Manchester City 2-0 ahead lit up The Hawthorns and was in complete contrast to the visitors' scrappy opener
There was no debate who the scorer was this time when Toure wrapped his foot around the ball to smash it into the top corner after swapping passes with Wilfried Bony
The midfielder will hope to have laid the foundations to a more consistent season this year
VIEW FROM THE BENCH
Manuel Pellegrini knows he must deliver this season and City sent out a clinical message to their title rivals
They were too strong for the Baggies and will have harder games, but Pellegrini will be pleased with their ruthless edge
Tony Pulis replaced debutant James McClean with Claudio Yacob at the break in a bid to stem the Manchester City tide, but it failed to rescue the game for the below-par Baggies
MOAN OF THE MATCH
Albion offered little resistance to City in the first half and it was over as a contest by the break
West Brom fans would have been looking for more fighting spirit from Pulis' side with the manager now crafting his own squad
But the Baggies never looked like getting back into the match once they fell behind
WHO'S UP NEXT
Watford v West Brom (Premier League, Saturday 15 August)
Manchester City v Chelsea (Premier League, Sunday 16 August)
Source : PA
Source: PA