Manchester City's Spanish manager Pep Guardiola reacts on the touchline during the UEFA Champions League, league phase day 4 football match between Sporting Lisbon and Manchester City at the Jose Alvalade stadium in Lisbon. AFP
Viktor Gyokeres's hat-trick and a series of costly City misses condemned Guardiola's men to three successive defeats for the first time since 2018.
Adding to City's misery was the sight of Sporting boss Ruben Amorim celebrating a remarkable victory in his final home game before leaving the Portuguese champions to take charge of Manchester United on November 11.
City's heaviest defeat since 2020 meant, for only the second time in the Guardiola era, they had suffered three consecutive losses in a single season.
After making a strong start to the season, the Premier League champions were beaten by Tottenham in the League Cup last week before losing at Bournemouth on Saturday in their first top-flight defeat since December.
City's unexpected malaise comes amid a rash of injuries to key players including Rodri, Ruben Dias, John Stones, Jack Grealish and Kevin De Bruyne, who was only fit enough for a brief substitute appearance at the Jose Alvalade stadium.
It was a painful return to Portugal for Lisbon-born Silva, who conceded City are mired in a damaging slump.
"It's disappointing because we're a bit in a dark place right now. Everything looks to be going in the wrong way," he said.
"Even when we are playing well we don't score our chances and we concede too easily.
"We need to get better very quickly otherwise it will be very difficult to come back from these losses.
"It's difficult to find reasons for what is happening to us. It just looks like this team is going the wrong way now.
"Our injured players need to come back because we need them and it's just not good enough tonight."
City's first defeat in four games in this season's Champions League should not be fatal to their European ambitions.
But Guardiola cannot fail to be alarmed by the way his injury-riddled defence was run ragged after Phil Foden put City ahead in the fourth minute.
'I like this challenge'
It didn't help that Jahmai Simpson-Pusey, a 19-year-old centre-back called up due to City's fitness problems, endured a baptism of fire in his first City start.
Erling Haaland's profligate finishing was equally culpable, with the Norway striker hitting the bar with a second-half penalty after missing several opportunities to increase City's advantage in the first half.
"We had a fantastic first half, now we are struggling to score. We create and concede when the opponents don't do much," Guardiola said.
"At 2-1 down, many things can happen. Emotionally we were not stable enough and in this competition you have to be stable.
"Sporting made a good moment, they were fast and scored. It can happen."
Pressed on the reasons for City's collapse, Guardiola admitted their creaky defence and injury issues were taking a toll.
"Maybe. When you play lots of games you cannot play the same line-up and same back four. We have had these problems for day one but it is what it is," he said.
"It is football. Maybe what we lived in the past is the exception. Sometimes you can lose. We were in the position where they punished us for the few they do and we struggled for the chances we had."
City desperately need to bounce back at Brighton in the Premier League on Saturday.
They are second in the table, two points behind leaders Liverpool, as they chase a fifth successive title and Guardiola insisted he can find an answer to their problems.
"Now is the difficult moment in terms of results but I want to be here. I want to fight and not give up," he said.
"I like this challenge as a manager I have ahead of me. Who wants to follow us will be there."
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