MANCHESTER, England -- Old and slow: They are two adjectives you do not usually associate with Manchester City, but as Manchester United inflicted the champions' fourth Premier League defeat of the season with a 2-1 victory at the Etihad, Pep Guardiola's players suddenly looked like precisely that.

That City looked so out of character was largely down to Ole Gunnar Solskjaer and his young United team, who, in the first half in particular, tore Guardiola's side apart with their blistering pace on the counterattack in the form of Marcus Rashford, Daniel James, Jesse Lingard and Anthony Martial. United, whose goals came from Rashford and Martial before half-time, were dominant in midfield too, with Scott McTominay outstanding once again as a defensive shield in front of the back four.

But while every visiting player produced arguably their best performance of the season, this was still a day when City looked like a shadow of their true selves.

Yet are their "true selves" now what we saw during the 179th Manchester derby? The evidence of the 90 minutes against United suggested that the City of the past two seasons -- the team that won the title with 100 points in 2017-18 before winning a domestic treble last term -- is no longer the one that we see out on the pitch.

For two seasons, Guardiola's City were incredibly consistent and one of the best teams of the Premier League era, but they now sit third in the table, 14 points behind runaway leaders Liverpool. The 32 points that City have banked so far is the lowest points total of Guardiola's managerial career after 16 games, so these are strange times for City and their manager.

"We need to keep clean sheets and strikers maybe need to put more away," City defender Kyle Walker said after the United defeat. "[United] had a game plan and it worked.

"You can't fault [Guardiola]. He has won numerous trophies. I can't put my finger on it."

Every team has its own cycle or shelf life, so perhaps we are now seeing the end of City's period of dominance. Liverpool look set to dethrone them as champions this season -- Jurgen Klopp's team are already European champions following last season's Champions League triumph -- and for the first time since Sir Alex Ferguson retired in 2013, United look like they may finally be on an upward trajectory again.

Tellingly, both Liverpool and United have beaten City this season by playing with pace on the counter. City remain a team that tries to beat opponents with a possession-based game, but their rivals have found a way to beat them, and that has coincided with Guardiola's team showing signs of wear and tear.

They failed to replace captain Vincent Kompany following the defender's summer move to Anderlecht -- a mistake that has haunted City since Aymeric Laporte was ruled out for six months with a knee injury earlier this season -- and this defeat against United also exposed the absence of a top-class left-back in Guardiola's squad. Benjamin Mendy's performances have led to Guardiola lacking trust in the Frenchman's defensive discipline, and neither Angelino nor Oleksandr Zinchenko has measured up in his place.

Fernandinho (34) and David Silva (33) are both expected to leave at the end of the season, while Sergio Aguero (31) is injured again and his replacement, Gabriel Jesus, has repeatedly shown himself to be incapable of filling in for the prolific Argentine. Raheem Sterling and Kevin De Bruyne are still world-class performers and both players are approaching the peak years of their careers, but two years ago, City had six or seven world-class players.

Now, they need to start planning for a rebuild because they cannot rely on Fernandinho, Silva and Aguero for much longer, and the youthful energy of United's players exposed the lack of zest within the City side.

Replacing personnel is one thing, but maintaining motivation is another challenge, and even the best managers have struggled to keep players hungry once they have won repeatedly. Ferguson achieved it at United for more than 20 years, but the Scot rebuilt his team perhaps four or five times. Guardiola has never stayed at a club long enough to do that even once, but if he remains at City beyond the end of this season, he will have to find a way to rebuild and ensure the desire is there to catch Liverpool and fend off a United revival.

Despite this defeat, the gap to Liverpool and his team's performances this season, Guardiola insisted after the game that he still believes in his City squad.

"I know who we are as a team," he said. "I am delighted to work with these guys. We have to think about what we have to do and think about the next game.

"It doesn't matter if it's six, eight or 14 points [behind Liverpool], we have to continue. We are a fantastic team."

Guardiola is right. This remains an outstanding City team, but perhaps their best days are behind them and a rebuild is needed.

United waited too long to build again at Old Trafford once Ferguson retired, and they are still paying the price for that. City need to heed the warning of their neighbours' mistake and avoid repeating it themselves.