After being right in the thick of it, the big-spending Blues now appear to be bit-part players.
One point from their last two games has left City eight points adrift of leaders Manchester United, having played a game more.
In addition they have required replays against lower league opposition to retain an interest in the FA Cup.
The reason is obvious.
After being one of the most difficult sides to score against earlier in the campaign, City's defence is now riddled with holes.
Since the goalless draw at Arsenal a month ago, the Blues have conceded 11 goals in six games and kept no clean sheets.
And Mancini accepts it is not a run that can continue for much longer if his side are going to challenge for honours.
"I would like this," said Mancini, when asked if his team needed to become more boring.
"When you don't concede a goal but you have players like Carlos (Tevez), (Edin) Dzeko, (David) Silva and Yaya Toure, you win 90% of your matches.
"At this moment, I would prefer it if we win 1-0 for two or three games.
"We would like to score two or three goals every game but it is not possible and in the past, all the teams that have won the title conceded very few goals."
Yet City have proved they can keep bigger clubs out.
Mancini's men ground out goalless draws against United and Arsenal in the last three months, just as they did at Tottenham on the season's opening day.
Chelsea and Liverpool also failed to score against them at Eastlands earlier in the campaign, leading to the accusation that City lack focus against the top flight's lesser lights.
"I don't think that is true," said Mancini.
"Our players know the value of this league very well. They know every game is a battle.
"Maybe we are having more difficulty when you meet teams that are at the bottom but this is normal.
"Three weeks ago everything was good but now we are in a bad moment because we concede too many goals.
"Maybe some situations have gone against us but it is important we understand it and try to have more concentration."
Mancini certainly is not blaming goalkeeper Joe Hart for the problem, even though plenty of critics have pointed the finger at England's number one.
"Joe is the best goalkeeper in England," said Mancini, playing down speculation that Hart might lose his place to Shay Given.
"If a striker doesn't score the game can finish 0-0. If a goalkeeper makes a mistake you might lose 1-0. That is the problem." A secondary issue for City is the loss of Adam Johnson for three months with an ankle injury.
Although Johnson has not been a regular starter this season, Mancini never underestimated the impact his former Middlesbrough winger could have.
"Players like Adam can change a game," he said. "He is a very important player for us and we don't have another like him."
As the extent of Johnson's injury was not known until the weekend, Mancini had little time to come up with an alternative.
Sebastian Larsson was mentioned but City have denied an offer was made to Birmingham.
Instead, they must head into the remainder of the campaign with the players they already had, with Mancini convinced United will drop enough points over the coming months to offer his side another opportunity.
"We have lost five points on United the last two games but it is possible they will lose two games," said Mancini.
"They have to play against Chelsea twice, against Arsenal and against us so anything can happen.
"All the teams at the top are very strong - United, Arsenal and Chelsea - but we want to stay there."
West Brom, meanwhile, will attempt to recreate their early season form when they take on Manchester City, according to head coach Roberto Di Matteo.
The Baggies acquitted themselves well against the likes of Manchester United and Liverpool during the first three months of the season.
And Di Matteo is hoping that the team can draw experience from their away win at Arsenal in September in particular.
He said: "We've had some good games and good results against the big teams so we're going to be positive.
"Even at home against Manchester United we matched them for long periods and we should have got something out of it."
Baggies midfielder Chris Brunt believes that his team only need look at the team's previous meeting, which City won 2-0, if they need motivation.
"We know we're in for a really tough game," he said. "They played very well against us at the Hawthorns and battered us from start to finish.
"They've got a good record at Eastlands so it's going to be a tough game, but it's one we're all looking forward to. They've got some of the biggest names in the world.
"It's a game that's going to be tough for us to get something out of, but we've proved that away from home against some of the big teams that we're capable of doing that."
However, Brunt concedes the Baggies do have one eye on their next few matches, in which they take on West Ham and Wolves at home, then Stoke and Birmingham away.
"There's games you're going to pinpoint more so than others," the Northern Ireland international said.
"We're going to Man City looking to try and get a result, but knowing that we've got a couple of big games coming up at home against teams that are down there around us.
"Those are ones we're going to have to look to take wins from, never mind draws."
Source: DSG
