Erling Haaland scored a hat-trick as Premier League champions Manchester City came from behind to beat Ipswich.
Few expected anything other than a comprehensive win for Pep Guardiola's Premier League juggernauts, but Sammie Szmodics sent the away fans wild on their first ever trip to the Etihad Stadium.
But Ipswich's first top-flight goal in 8,158 days merely lit a fire under the reigning champions, with Haaland scoring goals either side of a Kevin De Bruyne strike.
City's three goals came by the 16th minute - and within 193 seconds of each other - as ex-City goalkeeper Aro Muric made two costly errors after conceding from the penalty spot on his Town debut.
The Norway international went on to complete his 10th hat-trick in sky blue late in a second half that saw Gundogan receive a hero's welcome.
The treble-winning captain completed his return to the club on Friday following a year at Barcelona and was given a fantastic reception before and after coming on for his second debut.
It was a fine end to a day that began with a gut punch for City, who emerged past their Premier League, Club World Cup and Community Shield trophies as they celebrated a fourth straight league crown.
But Ipswich were undaunted by the task awaiting them, epitomised by Omari Hutchinson's driving run after Sam Morsy stopped a City attack.
The 20-year-old eventually played the ball inside to Ben Johnson, who brilliantly slipped in Szmodics to send a shot squirming through Ederson's legs and rolling over the line.
It was a shock seventh-minute opener followed by a relentless City response.
Leif Davis appeared to have got away with a challenge on Savinho, but VAR David Coote sent referee Sam Allison - promoted from fourth official after Michael Salisbury sustained an injury in the warm-up - to the monitor.
He pointed to the spot and Haaland struck the 12th-minute penalty past Muric, whose afternoon quickly got worse.
Two minutes later and the Ipswich debutant was dispossessed just inside his own box by Savinho, who steered into the path of De Bruyne to slam the ball into an empty net.
Muric was found wanting again in the 16th minute. This time he darted out trying to cut out a De Bruyne pass, only to see Haaland nod the ball beyond him.
It was quite the collapse by Ipswich, who saw the crossbar rattled by Rico Lewis and then De Bruyne as City threatened a fourth.
Haaland went close to completing a first-half hat-trick in stoppage time, before which Ipswich had strong claims for a penalty of their own after Savinho's clumsy challenge on Davis.
Mateo Kovacic pulled up hurt early in the opening stages of the second period that City continued on top, with Muric having to superbly push over a Haaland header from six yards.
Ipswich were defending well and Guardiola turned to his bench, with chants of 'Gundo's coming home' filling the air as Gundogan was introduced alongside Jack Grealish with 19 minutes remaining.
Play had long since petered out, but Haaland wanted another match ball for his collection and in the 87th minute he turned on the edge of the box and rifled a low effort beyond Muric's reach.
The Norway sharpshooter was immediately withdrawn by Guardiola.
