Nottingham Forest condemned Manchester City to a third straight Premier League loss as Enzo Maresca's side slipped further behind leaders Arsenal.
Despite starting the day in the Premier League's relegation zone, Forest triumphed 3-1 at the City Ground thanks to two goals from former City striker Liam Delap.
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It is the first time in two years that City have lost three straight in the league and the first time they have conceded three goals to a team that began the day in the Premier League's bottom three since September 2019.
City, who won seven straight games to start the season, remain in second place but are now six points behind leaders and titleholders Arsenal.
"We won the first seven in a row and that's never happened, and now we've lost three in a row -- it's football," City manager Maresca told Sky Sports. "We have to try to be better game after game."
The victory took Forest out of the relegation zone and sent Manchester United into the bottom three.
It could be a coming of age for both Delap and Forest, who had struggled to adapt to life under new boss Oliver Glasner, with just one win from their opening nine games.
Delap had scored once in his opening eight games following his club-record move from Chelsea, but his brilliant double suggested he can be the man to fire Forest to better things this season.
Delap began his career at City, but played just two Premier League games for the club.
City found themselves 2-0 down inside 20 minutes and trailed at halftime in a third consecutive Premier League game for the first time since 2007, before the club was taken over by Abu Dhabi United Group.
City's slump in form comes amid the backdrop of the ongoing appeal against Premier League charges; their season is showing signs of falling apart.
But Maresca, who replaced the club's most successful manager, Pep Guardiola, this summer insists it is too early to panic.
"I didn't know them before, and now it's three or four months that we are together," he said. "I think they need to know me and I need to know them. It's a learning journey.
"We know what we do well but we need to understand what we are not doing well and try to improve it."
Previously without a win in the league since April, Forest, got off to a dream start Saturday.
Jair Cunha caught City defender Josko Gvardiol in possession and he surged forward, finding a gap to slide the ball into the bottom left corner and give his team the lead in the sixth minute.
More defensive mishaps from City, which again lost the ball, allowed Delap to sprint from inside his own half and between two defenders before firing into the back of the net to double Forest's advantage in the 18th.
City managed to get one back early in the second half. Jérémy Doku latched onto a long ball over the top on the left flank and his cross was deflected into the path of Rayan Cherki, who drove it into the top left corner.
City were pushing hard for the equalizer, but Forest restored their two-goal advantage in the 74th, with Delap finishing off a rapid counterattack with a fine shot that went in off the inside of the far post.
Forest coach Glasner sprinted half the length of the field to celebrate with his players.
Information from ESPN Research, The Associated Press and PA contributed to this report.
