MANCHESTER, England -- David Moyes was once ridiculed for saying that Manchester United should aspire to be like Manchester City, but the former United manager was right when he said it in 2014 and it still rings true today, following another City derby win on Sunday -- 4-1 this time -- which restored the champions' six-point lead over Liverpool at the top of the Premier League.

Two goals apiece from Kevin De Bruyne and Riyad Mahrez -- Jadon Sancho had earlier equalised after De Bruyne's opener -- gave City a comfortable victory that was much more emphatic than the score line suggests. At one point during the second half, City amassed 92% of possession during a 15-minute period as United's players were tormented by the 'oles' of the home supporters.

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United were humiliated, with former captains Gary Neville and Roy Keane lambasting the performance in their roles as TV pundits. Neville said United "finished like an absolute shower" and "were a disgrace in the last 25 minutes," while Keane accused Ralf Rangnick's players of a "shameful" performance. "They gave up," Keane said.

Such condemnation is becoming a recurring theme whenever United play against a major rival. Already this season, they have lost 5-0 at home to Liverpool and then lost 2-0 against City at Old Trafford in a game that could have -- and maybe should have -- ended with Pep Guardiola's team winning by an even bigger margin than Liverpool.

There was once a time when United ruthlessly defeated their rivals on a regular basis, back in the days when Sir Alex Ferguson's team won 13 titles in 20 years. But those days are gone and Guardiola said after this game that United's decline is a warning to City and all other clubs who think their dominance will never end.

"United couldn't expect a decade ago so many years without titles," Guardiola said. "But this is a lesson we must learn too. You can't believe you are so good that what happened to United can't happen."

"It can change like that," he added, snapping his fingers. "I remember AC Milan, so many Champions Leagues and titles and then they have been so many years without playing in Europe. When I was a teenager, the team of Arrigo Sacchi was the best in the world, but it doesn't matter how big you are, it can happen."

It is a statistical anomaly that United had won four of their previous seven games against City prior to this defeat, but those victories never amounted to anything tangible. City, meanwhile, just continued to win titles. In contrast, United's last trophy came in 2017.

City are consistently exceptional. Their players perform to a clear plan constructed by Guardiola and his coaches, and they have a squad stocked with supremely talented players who are prepared to work harder than their opponents whenever they play.

United have a squad that cost almost as much as City's, but while the Blues get value for money, the Reds just throw it away by paying over the odds, repeatedly, for mediocre players. The likes of Aaron Wan-Bissaka, Victor Lindelof and Harry Maguire wouldn't come close to City's squad, but their collective transfer fees amount to a staggering £165 million, so it's not as if United have done anything on the cheap in recent years.

When Moyes made his remarks, it was following a 3-0 derby defeat at home to City in March 2014, when United were reigning champions, which ultimately helped the Blues beat Liverpool to the title that season. Moyes was fired within a month and United's tailspin of different managers and under-performing players continues, eight years on.

Where United have chopped and changed, City have enjoyed the stability of having Guardiola in charge for the last six years. Manuel Pellegrini was manager for three years prior to that, so there is a thread of consistency at City, which now shows itself on the pitch, where the players perform as if on auto-pilot. Their passing is unerringly accurate and they know how to win.

And they have players like De Bruyne, who has become as influential a midfielder in the Premier League as the likes of Keane, Patrick Vieira, Frank Lampard and Steven Gerrard before him.

United had no answer to De Bruyne in this game, with Fred and Scott McTominay ill-equipped to stop him. Paul Pogba, who has been at United as long as Guardiola has been at City, only with vastly different results, shone at times and delivered an exquisite pass for Sancho's goal, before being substituted in the second half after running out of steam.

City's players don't run out of steam, but winning teams tend to be blessed with players who are prepared to run all day.

That's what United lacked at the Etihad, and not for the first time this season. They have a group of players who can't be relied upon when the going gets tough, and whoever is appointed as the club's next permanent manager in the summer faces a mammoth challenge to get United competing again.

But the new boss won't have to look far for the perfect example of what a successful team looks like. Just like Moyes said, City are the team to aspire to.