After Albion spurned a golden chance through Semi Ajayi in the opening minutes, The Citizens turned on the style in the first half.
Two composed strikes from Ilkay Gundogan came either side of a controversial Joao Cancelo finish, that was flagged offside in the build-up and eventually given by VAR.
City were firmly in control and dominated possession, adding a fourth on the stroke of half-time through Riyad Mahrez.
The Baggies aimed to tighten up the defence at the break but instead Mahrez became the provider as he put the ball on a plate for Raheem Sterling to add a fifth goal after 57 minutes.
Albion’s worst ever Premier League defeats were 6-0 losses to Liverpool in April 2003 and Chelsea in August 2010, and with City showing signs of equaling or beating that record, the hosts sat back in the hope of nullifying them.
In the end that can be the only positive to take as they fell to a miserable 5-0 defeat.
Sam Allardyce made three changes to his Albion side following the defeat to West Ham, starting with a 4-5-1 formation.
Kyle Bartley, Conor Gallagher and Kamil Grosicki all dropped out - with the latter not making the squad.
Dara O’Shea moved to centre-back, allowing Darnell Furlong to come in at right-back. Robert Snodgrass also returned to the starting XI, as did Karlan Grant who made a speedy recovery from a fractured foot.
Pep Guardiola made two changes to the side that beat Aston Villa in their last Premier League game, starting in a 4-3-3 formation.
Kevin De Bruyne was absent from injury and was replaced by Mahrez, while Cancelo moved back to his more natural right-back position and Oleksandr Zinchenko came in at left-back.
As a result, Kyle Walker dropped to the bench.
Phil Foden, who entered the game in impressive form, made his 100th appearance for City.
Despite the 18-place gap in the league table between the teams ahead of kick-off, Albion had the first major chance of the game.
Within the opening two minutes a Furlong throw caused confusion in the City box and a Ajayi shot was blocked from six yards. There were suggestions of a Rodri handball in the build-up.
The visitors immediately sprung a counter-attack, however, and Foden found himself with plenty of space on the left wing. He cut inside and his curling effort was tipped onto the post by Sam Johnstone. It was a superb stop after the ball came through Furlong’s legs and took a deflection.
City continued to pile on the pressure and forced the opening goal within six minutes. Cancelo played a delightful 35-yard pass to Gundogan who, despite being in on goal, checked back and whipped a right-footed shot into the far left corner.
Guardiola’s men were enjoying themselves and dominating possession. In typical fashion for his team, the full-backs were moving inside into midfield regularly - with Cancelo at the heart of most attacks.
After 20 minutes the right-back curled in a wonderful effort from the edge of the box to make it two. Bernardo Silva was flagged offside in the build-up but after play continued and the goal was scored, a VAR check proved he was narrowly onside and the goal stood.
In a rare venture forward from Albion, Callum Robinson scuffed a shot narrowly wide from 18 yards, after some good build-up play got him in a promising position.
But in the 30th minute City added a third. Romaine Sawyers was sloppy with the ball on the edge of his own box and as Gundogan dispossessed him, the German skipped beyond O’Shea and tucked the ball into the bottom corner.
With half-time approaching the visitors added a fourth as Mahrez cut inside from the right and curled an effort into the far corner. It was the last major action of the half as City entered the break in control.
As the teams emerged for the second half Bartley replaced Robinson, meaning Albion changed to a back five.
City continued to dominate, however, and a powerful effort from 25-yards by Rodri clipped the top of the bar on it’s way over.
The visitors turned on the style after 57 minutes when a lofted pass by Rodri found Mahrez on the right. He crossed first time for Sterling who finished from close range.
Albion were rarely threatening as the game ticked beyond the 65th minute, despite the introduction of Hal Robson-Kanu and Matt Phillips. The lack of ball retention, particularly in midfield, was key to their inability to forge attacks.
Robson-Kanu, as Grant and Robinson were before him, was isolated up front as his team-mates camped behind him in a defensive shape, desperate not to concede a sixth.
In some respects the defensive lines were doing their job as they fought off several City attacks and set pieces. Phillips did have one opportunity to counter but his cross flattered to deceive.
As Allardyce was left slumped in his seat in the dugout his Albion side failed to threaten in the closing stages, and a weak shout for a penalty from Robson-Kanu was denied.
In the end Albion were condemned to their second 5-0 home defeat of the season.
West Brom: Johnstone, Furlong, Ajayi, O’Shea, Gibbs, Snodgrass (Phillips, 59), Sawyers, Livermore, Grant (Robson-Kanu, 64), Pereira, Robinson (Bartley, 45).
Subs not used: Button, Ivanovic, Peltier, Townsend, Gallagher, Edwards.
Man City: Ederson, Cancelo, Stones, Dias, Zinchenko, Gundogan (Laporte, 51), Rodri, Mahrez, Silva (Jesus, 61), Foden (Torres, 51), Sterling.
Subs not used: Steffen, Walker, Mendy, Fernandinho, Garcia, Bernabe.