Twelve years ago, Manchester City triggered a seismic shift in English football by beating treble-chasing Manchester United at Wembley.
Now City's own treble bid will come under threat from resurgent United in Saturday's FA Cup final.
With the Premier League wrapped up for a third successive season, City are two victories away from becoming only the second English club -- after United in 1999 -- to win the English title, the Champions League and the FA Cup in the same campaign.
City's current success and United's status as hopeful challengers would have been unimaginable when they last met in the FA Cup at Wembley in the 2011 semi-finals.
Just a few weeks after that showdown at the national stadium, United would clinch the Premier League title for the fourth time in five years, while also reaching the Champions League final.
In stark contrast to United's golden era under boss Alex Ferguson, City were still scarred by decades of dysfunction and they headed to Wembley in the midst of a trophy drought that had become a source of embarrassment.
Such was United's superiority over their neighbours that fans cheekily displayed a banner in the Stretford End at Old Trafford which showed how many years it was since City last won a trophy.
To the intense frustration of the blue side of Manchester, the number on the banner was 35 by 2011.
Yet by the time they left Wembley on a grey April afternoon, City had delivered a statement of intent that would soon render that mocking banner redundant.
The first Manchester derby to be played at Wembley was an appropriate setting for a defining moment in English football.
Since City were taken over by Sheikh Mansour's Abu Dhabi-based group in 2008, their vast spending on new players had become the talk of the Premier League.
Ferguson had dismissively waved away talk of City posing a threat to United when he dubbed their rivals “noisy neighbours” in 2009.
But City were gradually improving under boss Roberto Mancini and the FA Cup semi-final served as their coming of age.
After United missed several chances, Yaya Toure, one of City's expensive recruits, scored the only goal of a fiercely-contested clash seven minutes after half-time.
The defeatism that had plagued City for so long was removed in one fell swoop.
Joleon Lescott was part of the defence that kept United at bay and the centre-back recalls the match as game-changer for both clubs.
“That FA Cup semi-final was a real shift in belief as a club, for us as players and the fans, but also for United,” Lescott said.
“They realised we were a real threat. That was a real turning point. It really propelled us.”
City would go on win the FA Cup final against Stoke, banishing the trophy taunts from United and setting the stage for the start of a blue dynasty in Manchester.
Mancini's men thrashed United 6-1 at Old Trafford the following season and won the title at their rivals' expense thanks to Sergio Aguero's unforgettable late goal against QPR on the final day.
“We weren't just the noisy neighbours anymore, we were very loud!” Nigel De Jong, a member of that title-winning team, said.
Since beating United in the 2011 semi-final, City have won 15 major trophies, including seven Premier Leagues, as Pep Guardiola arrived to lead them to new heights with five titles in the last six seasons.
United have won only six major trophies in the same period with their last title coming in Ferguson's final season in 2013.
However, a revival could be brewing after United boss Erik ten Hag ended the club's six-year trophy drought this season.
Winning the League Cup and finishing third in the Premier League are encouraging signs, but beating the champions in the first all-Manchester FA Cup final would be an even more significant milestone.
“It's obvious we play against probably, at this moment, the best team, but still there is a chance. We have to give everything,” Ten Hag said.
And with their club seemingly on the verge of being bought by a wealthy new owner, United fans can dare to dream of emulating the City surge that started with an unexpected victory at Wembley over a decade ago.
Main photo: Manchester City won their third successive Premier League title, but eyes will surely be on the bigger achievement of winning the treble