However, after nine months of gruelling rehab, the German midfielder's comeback lasted just shy of an hour when an "industrial" hack from a lunging Claudio Yacob left him in a crumpled heap on the floor.
Pep Guardiola named Gundogan in his XI at The Hawthorns and he was instrumental in a dominant first-half showing, although the visitors were unable to add to Leroy Sane's third-minute opener before the break.
City were dominating possession, however, and they were twice denied a second goal in the 19th minute.
Yacob equalised to reward a much-improved West Brom display in the second period, although Sane settled matters with a fine 77th-minute victor.
The Cup match against West Brom was Gundogan's first start of the 2017-18 campaign.
The German celebrates his victor with Gabriel Jesus. Gareth McAuley started as he has recovered from a thigh injury.
"City got their free-kick, Yacob got booked".
Unfortunately for the England goalkeeper, Sane was on hand to fire in a technically superb effort to open the scoring.
But there was no hiding the total dominance of Guardiola's men, who statistics showed had enjoyed nearly 70 per cent of the first-half possession.
But the Albion striker glanced a header wide after drifting away from Mangala. He immediately signaled to the bench and was replaced by Kyle Walker in the 59th minute. Gundogan came on as a substitute for a 24-minute spell in the victory.
West Brom boss Tony Pulis defended Yacob when asked about his player's challenge.
It owed much to poor defending from City, who left both Yacob and Jonny Evans unmarked in the six-yard box to meet a Kieran Gibbs corner.
However, the Citizens took little time to reply and it was Sane again who was the hero, receiving the ball from Bernardo Silva before cutting in from the right and curling home from the edge of the area.