Ruben Amorim's Manchester United honeymoon is truly over after Nottingham Forest inflicted a second straight Premier League defeat on his side on Saturday while Manchester City stumbled again.
Amorim replaced the sacked Erik ten Hag at Old Trafford last month after a terrible start to the season.
He began brightly, with a draw and two wins in his first three games.
But reality is starting to bite hard after a 2-0 Premier League defeat at Arsenal in midweek followed by Saturday's chastening 3-2 loss to high-flying Forest, who capitalised on United's defensive blunders.
United forward Rasmus Hojlund cancelled out Nikola Milenkovic's early goal at Old Trafford, but Morgan Gibbs-White and Chris Wood put the visitors in charge. Forest kept the home side at bay after Bruno Fernandes pulled one back.
United's Andre Onana was embarrassed by a swerving Gibbs-White strike for Forest's second while the goalkeeper, Lisandro Martinez and Matthijs De Ligt all failed to deal with a looping Wood header for the third.
The win lifts Forest to fifth in the Premier League table. United are languishing in 13th spot.
"Tough game in a tough moment but we have to continue the job," a disappointed Amorim said.
"This is a long journey. We are improving in some aspects. We have to win games to help us improve the team.
"We are in the start of something so big that we pay attention to every detail. We already know it's a big job so we have to continue."
Forest boss Nuno Espirito Santo said "I'm very proud of the way we work together, build things together, from the owner to everyone else in the club.
"It's a moment to celebrate. But for me, I'm thinking about (next week's match against) Aston Villa."
Manchester City failed to win for the eighth time in nine games in a 2-2 draw at Crystal Palace.
Pep Guardiola's men had the chance to go second in the table but failed to build on an encouraging 3-0 win over Forest in midweek.
Daniel Munoz fired the home team ahead early but Erling Haaland's towering header levelled the score.
The visitors started the second half strongly but were hit with a sucker punch when Maxence Lacroix powered home Will Hughes' corner.
Rico Lewis found the top corner to level once more for City but was then sent off six minutes from time.